Redox-Active Metal-Organic Frameworks for the Catalytic Oxidation of Hydrocarbons

ABSTRACT

The disclosure provides for metal organic frameworks (MOFs) which comprise a plurality of redox-active metals or metal ions that are linked together by a plurality of dioxide-benzenedicarboxylate-based organic linking ligands. The disclosure further provides for the use of these MOFs in variety of applications, including catalyzing the oxidization of various hydrocarbons to higher oxidation states.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 from ProvisionalApplication Ser. No. 62/161,374, filed May 14, 2015, the disclosure ofwhich is incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention was made with government support under Grant No.DE-SC0008688 and Grant No. DE-AC02-05CH11231 awarded by the UnitedStates Department of Energy. The government has certain rights in theinvention.

TECHNICAL FIELD

The disclosure provides for metal organic frameworks (MOFs) whichcomprise a plurality of redox-active metals or metal ions that arelinked together by a plurality of dioxide-benzenedicarboxylate-basedorganic linking ligands. The disclosure further provides for the use ofthese MOFs in variety of applications, including catalyzing theoxidization of various hydocarbons to higher oxidation states.

BACKGROUND

Metal-organic frameworks (MOFs) are porous crystalline materials thatare constructed by linking metal clusters called Secondary Binding Units(SBUs) and organic linking ligands. MOFs have high surface area and highporosity which enable them to be utilized in diverse fields, such as gasstorage, catalysis, and sensors.

The selective and efficient conversion of light alkanes into value-addedchemicals remains an outstanding challenge with tremendous economic andenvironmental impact, especially considering the recent worldwideincrease in natural gas reserves. In nature, C—H functionalization iscarried out by copper and iron metalloenzymes, which activate dioxygenand, through metal-oxo intermediates, facilitate two- or four-electronoxidations of organic substrates.

SUMMARY

The disclosure three-dimensional metal-organic frameworks (MOFs) thatcomprise a plurality of redox active metals or metal ions connected by aplurality of 2,5-dioxido-1,4-benzenedicarboxylate (dobdc⁴⁻) and/or2,4-dioxido-15-benzenedicarboxylate (m-dobdc⁴⁻) based organic linkingligands. The MOFs of the disclosure are stable to desolvation andcomprise coordinatively-unsaturated redox active metal centers in asingle, well-defined environment. In a particular embodiment, thedisclosure provides for a Fe₂(dobdc) (1) based framework, whichhexagonal pore channels of the framework are lined with a single type ofsquare pyramidal iron(II) site (see FIG. 3A). The high density andredox-active nature of these open metal sites engender excellent O₂/N₂and hydrocarbon separation properties. The disclosure demonstrates thereactivity of MOFs of the disclosure towards a gaseous two-electronoxidant and O-atom transfer agent (e.g., N₂O), generating a highlyreactive iron(IV)-oxo species capable of oxidizing strong C—H bonds. Ina further embodiment, the MOFs disclosed herein, catalyze the oxidationof light hydrocarbons (e.g., methane, ethane, and propane) intocorresponding alcohols and/or aldehydes; catalyze the oxidation ofcyclohexane into KA oil (i.e., a mixture of cyclohexanol andcyclohexanone); catalyze the oxidation of benzene to phenol; andcatalyze the oxidation of alkenes to corresponding epoxides (e.g.,propylene to propylene oxide, and ethylene to ethylene oxide).

The disclosure also provides that the MOFs of the disclosure may also becomprised of a plurality of redox-inactive metals or metal ions inaddition to the redox-active metal or metal ions (i.e., mixed-metalMOFs). In a further embodiment, the mixed MOFs of the disclosure arehighly selective catalysts which allow for the conversion of(C₁-C₆)-hydrocarbons to corresponding alcohols versus other oxidativeproducts.

In a particular embodiment, the disclosure provides for a MOF thatcomprises a plurality of redox-active metals or metal ions connected bya plurality of organic linking ligands comprising the structure(s)selected from the group consisting of:

wherein R¹-R¹⁴ are independently selected from H, D, optionallysubstituted FG, optionally substituted (C₁-C₂₀) alkyl, optionallysubstituted (C₁-C₁₉) heteroalkyl, optionally substituted(C₁-C₂₀)alkenyl, optionally substituted (C₁-C₁₉) heteroalkenyl,optionally substituted (C₁-C₁₉)alkynyl, optionally substituted(C₁-C₁₉)heteroalkynyl, optionally substituted (C₁-C₁₉)cycloalkyl,optionally substituted (C₁-C₁₉)cycloalkenyl, optionally substitutedaryl, optionally substituted heterocycle, optionally substituted mixedring system, wherein one or more adjacent R groups can be linkedtogether to form one or more substituted rings selected from the groupcomprising cycloalkyl, cycloalkenyl, heterocycle, aryl, and mixed ringsystem.

In one embodiment, the organic linking ligand comprises a structureselected from the group consisting of:

wherein

In a specific embodiment, the organic linking ligand is selected from:

In all of the foregoing embodiments, the MOF is capable of catalyticallyoxidizing (C₁-C₆)-hydrocarbons to their corresponding alcohols, epoxidesand/or aldehydes. In a further embodiment, the MOF comprises repeatingunits of a metal (e.g., M¹) linked through a carboxylate to the linkingligand. For example, in certain embodiment the MOF comprises repeatingunits of the formula (M¹)₂(dobdc) and/or of the formula (M¹)₂(m-dobdc),wherein M¹ is a redox-active metal or metal ion. In yet a furtherembodiment, the redox-active metal is selected from Fe, Mn, Co, Ni, andCu, or a divalent cation of any of the foregoing.

In another embodiment, the disclosure also provides for a MOF that is amixed metal MOF comprising a plurality of redox-active metals or metalions and a plurality redox-inactive metals or metal ions that areconnected by a plurality of organic linking ligands comprising thestructure(s) selected from the group consisting of:

wherein R¹-R¹⁴ are independently selected from H, D, optionallysubstituted FG, optionally substituted (C₁-C₂₀) alkyl, optionallysubstituted (C₁-C₁₉) heteroalkyl, optionally substituted(C₁-C₂₀)alkenyl, optionally substituted (C₁-C₁₉) heteroalkenyl,optionally substituted (C₁-C₁₉)alkynyl, optionally substituted(C₁-C₁₉)heteroalkynyl, optionally substituted (C₁-C₁₉)cycloalkyl,optionally substituted (C₁-C₁₉)cycloalkenyl, optionally substitutedaryl, optionally substituted heterocycle, optionally substituted mixedring system, wherein one or more adjacent R groups can be linkedtogether to form one or more substituted rings selected from the groupcomprising cycloalkyl, cycloalkenyl, heterocycle, aryl, and mixed ringsystem. In one embodiment, the organic linking ligand comprises astructure selected from the group consisting of:

wherein:

In a specific embodiment, the organic linking ligand is selected from:

wherein, the MOF is capable of catalytically oxidizing of smallhydrocarbons to their corresponding alcohols and aldehydes. In a furtherembodiment, the plurality of redox-inactive metal ions is selected fromMg, Ca, Sr, Ba, Sc, Y, Ti, Zr, V, Nb, Ta, Cr, Mo, W, Re, Ru, Os, Rh, Ir,Pd, Pt, Ag, Au, Zn, Cd, Hg, Al, Ga, In, Si, Ge, Sn, Pb, As, Te, La, Ce,Pr, Nd, Sm, Eu, Gd, Tb, Db, Tm, Yb, and La, or a divalent cation of anyof the foregoing.

In another embodiment, the disclosure further provides for a MOF thatcomprises repeating units of the formula (M¹)(M²)_(2-x)(linking ligand)and/or of the formula (M¹)_(x)(M²)_(2-x)(linking ligand),(M¹)_(x)(M²)_(2-x)(dobdc) and/or of the formula(M¹)_(x)(M²)_(2-x)(m-dobdc), wherein at least one of M¹-M² is aredox-active metal or metal ion, x is a number less than or equal to 1,0.3, or 0.1. In yet another embodiment, M¹ is selected from Fe, Mn, Co,Ni, and Cu, or a divalent cation of any of the foregoing. In yet anotherembodiment, M² is selected from Mg, Ca, Sr, Ba, Sc, Y, Ti, Zr, V, Nb,Ta, Cr, Mo, W, Re, Ru, Os, Rh, Ir, Pd, Pt, Ag, Au, Zn, Cd, Hg, Al, Ga,In, Si, Ge, Sn, Pb, As, Te, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Db, Tm, Yb,and La, or a divalent cation of any of the foregoing.

In a particular embodiment, the disclosure provides for a MOF of thedisclosure, wherein the MOF is reacted with a terminal oxidant, such asN₂O. In a further embodiment, a MOF disclosed herein is reacted with N₂Oat a temperature of about 75° C. and at a pressure between 1 to 10 bar.

In a certain embodiment, the disclosure also provides for a catalyticdevice comprising a MOF disclosed herein. In a further embodiment, thedevice comprises a column or bed which comprises a MOF of thedisclosure.

In a particular embodiment, the disclosure further provides methods foroxidizing a molecule or compound, comprising contacting the molecule orcompound with a MOF disclosed herein. In another embodiment, themolecule or compound is a C₁-C₆ alkane, a C₁-C₆ alkene, a C₁-C₆ alkyne,benzene, or a C₃-C₆ cycloalkyl. In a further embodiment, a C₁-C₆ alkaneis converted to a corresponding C₁-C₆ alcohol or C₁-C₆ aldehyde bycontacting the C₁-C₆ alkane with a MOF disclosed herein. In yet afurther embodiment, a C₁-C₆ alkane is selectively converted to the C₁-C₆alcohol versus the C₁-C₆aldehyde in a ratio of 20:1 by contacting theC₁-C₆ alkane with a MOF disclosed herein. In another embodiment, a C₁-C₆alkene is converted to a C₁-C₆ corresponding epoxide by contacting theC₁-C₆ alkene with a MOF disclosed herein. In yet another embodiment,cyclohexane is converted into KA oil by contacting cyclohexane with aMOF disclosed herein.

DESCRIPTION OF DRAWINGS

FIG. 1 diagrams a M₂(dobdc)-based framework showing a close-up of a SBUand the oxidation of ethane molecule to ethanol via oxidation by theframework.

FIG. 2A-C provides (A) Structure of the metal-organic frameworkM₂(dobdc), showing hexagonal channels lined with 5-coordinate M²⁺ sites.The view is down the c axis, along the helical chains of M²⁺ ions.M²⁺=yellow; oxygen=red; carbon=gray; hydrogen atoms not shown forclarity. (B) Structure of the ligand, dobdc⁴⁻. (C) Structure of theligand m-dobdc⁴⁻ which forms a similar framework M₂(m-dobdc) that alsohas hexagonal channels lined with open metal sites.

FIG. 3A-B presents the structure of bare and N₂O-dosed Fe₂(dobdc). (A)Structure of Fe₂(dobdc), showing hexagonal channels lined with5-coordinate iron(II) sites. The view is down the c axis, along thehelical chains of iron(II) ions. (B) Experimental structures for N₂Obinding in Fe₂(dobdc) loaded with 0.35 equivalents of N₂O at roomtemperature and then slowly cooled to 10 K. N₂O binds with a bent Fe—N₂Oangle, with a mixture of 60% η¹-O coordination and 40% η¹-Ncoordination. For comparison of calculated structures with experimental,see FIG. 4A-B.

FIG. 4A-B provides a comparison of the experimental and theoreticalstructures of N₂O adducts of Fe₂ (dobdc). (A) η¹-O coordination of theN₂O molecule. (B) η¹-N coordination of the N₂O molecule. All distancesare in Å and all angles are in degrees. Shown are N, O and, Fe(experiment) or Fe (theory).

FIG. 5 presents powder X-ray (PXRD) diffraction patterns forFe_(0.1)Mg_(1.9) (dobdc) before (bottom) and after (top) N₂O/ethanetreatment.

FIG. 6 shows the unit cell of Fe_(0.1)Mg_(1.9) (dobdc). X-ray powderdiffraction data obtained from a sample of Fe_(0.1)Mg_(1.9) (dobdc).a=25.9485 (9) Å′, c=6.8574 (4) Å′, and V=3998.7 (3) Å. The crosses andtop line represent the experimental and calculated diffraction patterns,respectively. The bottom line represents the difference betweenexperimental and calculated patterns. The data were collected at 298 K.

FIG. 7 provides a Rietveld refinement (100 K) of Fe₂(OH)₂(dobdc). X-raypowder diffraction data obtained from a sample of Fe₂(OH)₂(dobdc). Themiddle line, crosses, and top line represent the background,experimental, and calculated diffraction patterns, respectively. Thebottom line represents the difference between experimental andcalculated patterns. The data were collected at 100 K.

FIG. 8 provides a Rietveld refinement (298 K) of Fe₂(OH)₂(dobdc). X-raypowder diffraction data obtained from a sample of Fe₂(OH)₂(dobdc). Themiddle line, crosses, and top line represent the background,experimental, and calculated diffraction patterns, respectively. Thebottom line represents the difference between experimental andcalculated patterns. The data were collected at 298 K.

FIG. 9 provides a Rietveld refinement (10 K) of bare Fe₂(dobdc). Neutronpowder diffraction data obtained from bare Fe₂(dobdc) at 10 K. Themiddle line, crosses, and top line represent the background,experimental, and calculated diffraction patterns, respectively. Thebottom line represents the difference between experimental andcalculated patterns.

FIG. 10 provides a Rietveld refinement (10 K) of Fe₂(dobdc) (N₂O)_(0.7).Neutron powder diffraction data obtained from Fe₂(dobdc) loaded withapproximately 0.35 N₂O per Fe²⁺. The middle line, crosses, and top linerepresent the background, experimental, and calculated diffractionpatterns, respectively. The bottom line represents the differencebetween experimental and calculated patterns. The data were collected at10 K.

FIG. 11 provides a Rietveld refinement (10 K) of Fe₂(dobdc) (N₂O)_(1.2).Neutron powder diffraction data obtained from Fe₂(dobdc) loaded withapproximately 0.6 N₂O per Fe²⁺. The middle line, crosses, and top linerepresent the background, experimental, and calculated diffractionpatterns, respectively. The bottom line represents the differencebetween experimental and calculated patterns.

FIG. 12 provides a Rietveld refinement (10 K) of Fe₂(dobdc) (N₂O)_(2.5).Neutron powder diffraction data obtained from Fe₂(dobdc) loaded withapproximately 1.25 N₂O per Fe²⁺. The middle line, crosses, and top linerepresent the background, experimental, and calculated diffractionpatterns, respectively. The bottom line represents the differencebetween experimental and calculated patterns. The data were collected at10 K.

FIG. 13 shows a Fourier difference map of Fe₂(dobdc) (N₂O)_(0.6).Fourier Difference Map of data obtained from Fe₂(dobdc) loaded with 0.35N₂O per Fe²⁺. Globules represent excess scattering density in thechannels of the framework that result from N₂O molecules binding at theFe²⁺ site.

FIG. 14 shows a Fourier difference map of Fe₂(dobdc) (N₂O)_(2.5).Fourier Difference Map of data obtained from Fe₂(dobdc) loaded with 1.25N₂O per Fe²⁺. Globules represent excess scattering density in thechannels of the framework that result from N₂O molecules binding at theFe²⁺ site. There is a slight rearrangement from the site I N₂Oorientation, denoted site Ia, upon population of the secondaryadsorption site.

FIG. 15A-B provides (A) FTIR spectra of Fe₂(dobdc) outgassed at roomtemperature 2 h (black curve) and activated at 433 K for 18 h (redcurve) and in contact with 40 mbar of N₂O at room temperature (bluecurve). The spectrum of the activated sample clearly shows thedisappearance of all features associated with methanol, with all otherbands unchanged. (B) FTIR spectra (background subtracted) in the2280-2160 cm⁻¹ spectral range of Fe₂(dobdc) in contact with 40 mbar ofN₂O (blue curve) and following progressive desorption at roomtemperature (light grey curves). A clear maximum is seen at 2226 cm⁻¹.The dotted blue line represents the spectrum of 40 mbar of gaseous N₂Oin the same spectral range.

FIG. 16A-B provides In situ transmission-mode FTIR spectra of Fe₂(dobdc)(green) and Fe₂(OH)₂(dobdc) (red). A thin film of Fe₂(dobdc) wasactivated at 433 K for 18 h (red curve), in contact with 180 mbar of N₂Oat room temperature (blue curve) and heated at 60° C. for 14 hours(green curve). Inset (A): background subtracted spectra illustrating theν (N—N) region and inset (B) magnification of 730-610 cm⁻¹ spectralrange, testifying the formation of Fe₂(OH)₂(dobdc).

FIG. 17A-B presents the results of CO titration experiments before andafter heating Fe₂(dobdc) in the presence of N₂O. (A) CO dosed on anactivated sample of bare Fe₂(dobdc) (B) CO dosed on a sample that hascontacted N₂O at room temperature for one day, and then overnight at 60°C. shows that the number of open Fe(II) sites has been reduceddramatically (less than 10% remaining).

FIG. 18A-B provides for the preparation and Mössbauer spectrum ofFe₂(OH)₂(dobdc). (A) Reaction scheme for the preparation of 2 fromFe₂(dobdc). (B) Mössbauer spectrum of 2, with the fit in black. The redcomponent has parameters consistent with high-spin Fe(III) (5=0.40(2)mm/s, IAEQ, =0.96(1) mm/s, area=80(2)%). A minor component (green) isassigned as unreacted Fe(II) sites, and another minor component (purple)is assigned as an amorphous Fe(III) decomposition product.

FIG. 19 provides an ATR-FTIR spectra of Fe₂(OH)_(0.6)(dobdc) (black) andFe₂(¹⁸OH)_(0.6)(dobdc) (dotted red).

FIG. 20A-B provides the structure and infrared spectrum ofFe₂(OH)₂(dobdc). (A) Infrared spectrum of a partially oxidized sample,Fe₂(OH)_(0.6)(dobdc) (black) and Fe₂(¹⁸OH)_(0.6)(dobdc) (dotted red).The peaks at 667 and 3678 cm⁻¹ shift to 639 and 3668 cm⁻¹, respectively,upon ¹⁸O labeling. (B) The structure of Fe₂(OH)₂(dobdc) obtained bypowder X-ray diffraction data (100 K). Selected interatomic distances(A) for 1: Fe—O1=1.92(1); Fe—O2=2.01(1); Fe—O3=2.08(1); Fe—O4=2.04 (1);Fe—O5=2.04(1); Fe—O6=2.20(1); Fe—Fe=3.16(1).

FIG. 21 provides a N₂ adsorption isotherm in Fe₂(OH)₂(dobdc) at 77 K.

FIG. 22 presents a BET plot of the N₂ adsorption isotherm inFe₂(OH)₂(dobdc) at 77 K. The black line represents a linear best fit ofthe data points (circles). Inset: parameters for the linear best fit andresulting constants for calculation of the BET surface area.

FIG. 23 provides a N₂ adsorption isotherm in Fe_(0.1)Mg_(1.9) (dobdc) at77 K.

FIG. 24 presents a BET plot of the N₂ adsorption isotherm inFe_(0.1)Mg_(1.9) (dobdc) at 77 K. The black line represents a linearbest fit of the data points (circles). Inset: parameters for the linearbest fit and resulting constants for calculation of the BET surfacearea.

FIG. 25 demonstrates N₂O activation and reactivity of Fe₂(dobdc).

FIG. 26 provides a structure and qualitative molecular orbital (MO)diagram for Fe₂(O)₂(dobdc). DFT and CASSCF/PT2 studies predict a shortiron-oxo bond (1.64 Å) and a high-spin, S=2 spin ground state foriron(IV)-oxos installed in the Fe₂(dobdc) framework. Selectedinteratomic distances (A) for 1: Fe—O1=1.638; Fe—O2=2.004; Fe—O3=2.127;Fe—O4=2.019; Fe—O5=2.054; Fe—O6=2.140.

FIG. 27 presents a wireframe representation of the cluster model for 4(89-atom cluster model). Highlighted in ball and stick, the Fe atom andits first coordination sphere and the Zn centers. The 90-atom clustermodel for 2 is similar, except 01 is replaced with an OH. Shown are: Fe;Zn; O; C and H.

FIG. 28A-D shows (A) Structure of the metal-organic framework M₂(dobpdc)(dobpdc⁴⁻=4,4′-dioxidobiphenyl-3,3′-dicarboxylate), showing hexagonalchannels lined with 5-coordinate M²⁺ sites. The view is down the c axis,along the helical chains of M²⁺ ions. M²⁺=yellow; oxygen=red;carbon=gray; hydrogen atoms not shown for clarity. (B) Structure of theligand, dobpdc⁴⁻. (C) Structure of a substituted ligand of (B) and (D) a3-ring variations of the expanded linkers.

FIG. 29A-B shows (A) A reaction scheme. The framework is combined with 5to 20 equiv of the oxidant, tBuSO₂PhIO, and 150 equiv. of cyclohexane,to form cyclohexanol and cyclohexanone. (B) A:K ratios obtained fromFe₂(dotpdc)^(R) (R=H, F, CH₃, and tBu). For the unsubstitutedderivative, the A:K ratio is roughly 3:1; however, this changes togreater than 8:1 for the tBu-functionalized ligand.

DETAILED DESCRIPTION

As used herein and in the appended claims, the singular forms “a,”“and,” and “the” include plural referents unless the context clearlydictates otherwise. Thus, for example, reference to “an organic linkingligand” includes a plurality of such linking ligands and reference to“the metal ion” includes reference to one or more metal ions andequivalents thereof known to those skilled in the art, and so forth.

Also, the use of “or” means “and/or” unless stated otherwise. Similarly,“comprise,” “comprises,” “comprising” “include,” “includes,” and“including” are interchangeable and not intended to be limiting.

It is to be further understood that where descriptions of variousembodiments use the term “comprising,” those skilled in the art wouldunderstand that in some specific instances, an embodiment can bealternatively described using language “consisting essentially of” or“consisting of.”

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood to one of ordinary skill inthe art to which this disclosure belongs. Although any methods andreagents similar or equivalent to those described herein can be used inthe practice of the disclosed methods and compositions, the exemplarymethods and materials are now described.

All publications mentioned herein are incorporated herein by referencein full for the purpose of describing and disclosing the methodologies,which are described in the publications, which might be used inconnection with the description herein. With respect to any term that ispresented in one or more publications that is similar to, or identicalwith, a term that has been expressly defined in this disclosure, thedefinition of the term as expressly provided in this disclosure willcontrol in all respects.

Metal-organic frameworks (MOFs) are porous crystalline materials thatare constructed by the linkage of inorganic metal clusters calledsecondary building units (SBUs) with organic linkers. These materialshave very large surface areas and pore volumes.

The selective and efficient conversion of light alkanes into value-addedchemicals remains an outstanding challenge with tremendous economic andenvironmental impact, especially considering the recent worldwideincrease in natural gas reserves. In nature, C—H functionalization iscarried out by copper and iron metalloenzymes, which activate dioxygenand, through metal-oxo intermediates, facilitate two- or four-electronoxidations of organic substrates. Duplicating this impressive reactivityin synthetic systems has been the focus of intense research. Inparticular, iron(IV)-oxo complexes have now been structurallycharacterized in various geometries (octahedral, trigonal bipyramidal)and spin states (S=1, S=2), and have proven to be competent catalystsfor a variety of oxygenation reactions. However, in the absence of aprotective protein superstructure, terminal iron-oxo species are highlysusceptible to a variety of decomposition pathways, includingdimerization to form oxo-bridged diiron complexes, intramolecular ligandoxidation, and solvent oxidation. Tethering a molecular iron species toa porous solid support such as silica or polystyrene could potentiallyprevent many of these side-reactions. In practice, however, complexesheterogenized in this manner are challenging to characterize byavailable techniques, and additional problems associated with stericcrowding, site inaccessibility, and metal leaching inevitably arise.Iron cations can also be incorporated into zeolites, either as part ofthe framework or at extraframework sites, producing reactive ironcenters that have no direct molecular analogue. Fe-ZSM-5, for example,has been shown to oxidize methane to methanol stoichiometrically whenpretreated with nitrous oxide. However, characterization of thesematerials is nontrivial due to the presence of multiple iron species,and the nature of the active sites in Fe-ZSM-5 remains largely a matterof speculation.

The use of a metal-organic framework to support isolated terminaliron-oxo moieties is a currently unexplored yet highly promising area ofresearch. The high surface area, permanent porosity, chemical andthermal stability, and synthetic tunability displayed by many of thesematerials makes them appealing in this regard. Additionally,metal-organic frameworks are typically highly crystalline withwell-defined metal centers suited for characterization by single crystaland/or powder diffraction techniques. Furthermore, while moleculariron(IV)-oxo complexes generally utilize nitrogen-based chelatingligands, the metal cations in metal-organic frameworks are often ligatedby weaker-field ligands, such as carboxylates and aryloxides, which areconstrained in their coordination position by the extended frameworkstructure. Thus, in addition to increased stability, terminal oxos inthese materials might also have novel electronic properties andreactivity imparted by their unique coordination environment.

While spectroscopic and theoretical studies have long attributed thereactivity of non-heme enzymatic and synthetic iron(IV)-oxo complexes toa quintet spin state, only a small handful of mononuclear high-spiniron(IV)-oxo species have been characterized, with all but oneexhibiting a trigonal bipyramidal coordination geometry. In thesesystems, the oxo moiety is either extremely unstable-[Fe(O) (H₂O)₅]2⁺,for example, has a half life of roughly 10 s or is inaccessible tosubstrates due to bulky ligand scaffolds, leading to sluggishreactivity. On the other hand, the Fe₂(dobdc) framework featuressterically accessible, site-isolated metal centers entrenched in aweak-field ligand environment. Utilizing these two properties, it ispossible not only to generate such a species, albeit fleetingly, butalso to direct it towards the facile activation of one of the strongestC—H bonds known.

Accordingly, The disclosure provides for metal-organic frameworks (MOFs)comprising a plurality of redox-active metals or metal ions linkedtogether with a plurality of organic linking moieties comprising thestructure(s) selected from the group consisting of:

wherein R¹-R¹⁴ are independently selected from H, D, optionallysubstituted FG, optionally substituted (C₁-C₂₀) alkyl, optionallysubstituted (C₁-C₁₉) heteroalkyl, optionally substituted(C₁-C₂₀)alkenyl, optionally substituted (C₁-C₁₉) heteroalkenyl,optionally substituted (C₁-C₁₉)alkynyl, optionally substituted(C₁-C₁₉)heteroalkynyl, optionally substituted (C₁-C₁₉)cycloalkyl,optionally substituted (C₁-C₁₉)cycloalkenyl, optionally substitutedaryl, optionally substituted heterocycle, optionally substituted mixedring system, wherein one or more adjacent R groups can be linkedtogether to form one or more substituted rings selected from the groupcomprising cycloalkyl, cycloalkenyl, heterocycle, aryl, and mixed ringsystem. In one embodiment, the organic linking ligand comprises astructure selected from the group consisting of:

wherein

In a specific embodiment, the organic linking ligand is selected from:

(dobdc⁴⁻=2,5-dioxido-1,4-benzenedicarboxylate,m-dobdc⁴⁻=2,4-dioxido-1,5-benzenedicarboxylate). In all of the foregoingembodiments, the MOF is capable of catalytic oxidation of a hydrocarbon(e.g., (C₁-C₆)-hydrocarbons) to higher oxidation states (e.g., catalyticoxidation of small hydrocarbons to their corresponding alcohols andaldehydes).

In a further embodiment, the disclosure provides for MOFs that arecomprised of a plurality of different redox active metals or metal ionslinked together by a plurality of linking moieties of the disclosure(e.g., dobdc⁴⁻ and/or m-dobdc⁴⁻ linking moieties). In yet a furtherembodiment, a MOF disclosed herein is comprised of a plurality ofredox-active metal or metal ions and a plurality of redox-inactive metalor metal ions, which are linked together bydioxido-benzenedicarboxylate-based organic linking moieties ordihydrooxyterphenyldicarboxylate-based linking moieties. In yet afurther embodiment, a MOF of the disclosure (e.g., a mixed metal MOF) ishighly selective for catalytically oxidizing an alkane to itscorresponding alcohol (e.g., a light weight alkane (e.g., C₁-C₆ alkane)to a corresponding alcohol) over other oxidative products (e.g.,carbonyls, epoxides, and carboxylic acids). In a particular embodiment,a MOF disclosed herein catalyzes the oxidation of a light weight alkaneto alcohol versus other oxidative products in a ratio of 2:1, 5:1, 10:1,15:1, 20:1, 25:1, 30:1, 35:1, 50:1, or 99:1, or in range that falls inbetween any of the foregoing. For example, a mixed metal MOF disclosedherein can selectively catalyze the oxidation of ethane to ethanolversus acetaldehyde in a 25:1 ratio.

Suitable alkanes that can be oxidized by the methods and compositions ofthe disclosure include methane (CH₄), ethane (C₂H₆), propane (C₃H₈),butane (C₄H₁₀), pentane (C₅H₁₂), hexane (C₆H₁₄), heptane (C₇H₁₆), octane(C₈H₁₈), nonane (C₉H₂₀), decane (C₁₀H₂₂), undecane (C₁₁H₂₄), anddodecane (C₁₂H₂₆). The methods include not only a single compound, butalso combinations of compounds, such as solutions, mixtures and othermaterials which contain at least one alkane. Foralkane/alkene-substrates, propane, propene, ethane, ethene, butane,butene, pentane, pentene, hexane, hexene, cyclohexane, octane, octene,styrene, p-nitrophenoxyoctane (8-pnpane), and various derivativesthereof, can be used. The term “derivative” refers to the addition ofone or more functional groups to an alkane, including, but not limited,alcohols, amines, halogens, thiols, amides, carboxylates, etc.

In a certain embodiment, the disclosure provides for reacting the MOFdisclosed herein with a terminal oxidant, such as N₂O, to generate a M²⁺redox-active metal center (e.g., Fe²⁺, Mn^(2+,) Co²⁺, Ni²⁺, and Cu²⁺).The oxidation can be carried out at low temperatures (about 75° C.) andat low pressures (1 to 10 bar). Accordingly, the MOF disclosed hereincan utilize very inexpensive oxidants in thermodynamically favorableconditions without having to use adjuvants, like acids. For example, itwas shown herein that the high-spin iron(II) centers within Fe₂(dobdc)(dobdc⁴⁻=2,5-dioxido-1,4-benzenedicarboxylate) can activate N₂O, mostlikely forming a transient, high-spin iron(IV)-oxo intermediate, whichrapidly reacts to afford Fe₂ (OH)₂(dobdc). Significantly, themagnesium-diluted analogue, Fe_(0.1)Mg_(1.9) (dobdc), is found toselectively oxidize ethane to ethanol in the presence of N₂O under mildconditions.

Currently, no widespread commercial process exists for the selectiveoxidative conversion of hydrocarbons into value-added chemicalfeedstocks such as methanol, ethanol or propanol. Industrially, methanolis produced in an indirect and energy intensive processes beginning withthe steam reformation of natural gas; ethanol is largely produced fromthe acid-catalyzed hydration of ethylene, which itself is produced bysteam cracking. The selective hydroxylation of, e.g., C₁ to C₃,hydrocarbons by the MOFs disclosed herein presents a large environmentaland economic impact. More so, when one considers the dramatic worldwideincrease in using shale gas reserves, which consists largely of methanebut also contains a significant amount of ethane and other light alkaneimpurities. The metal-organic framework disclosed herein are capable ofoxidizing ethane into its various oxygenates when heated to 75° C. inthe presence of nitrous oxide. Products include ethanol, acetaldehyde,and ether oligomers. Much greater selectivity, however, can be achievedwhen using a mixed metal MOF of the disclosure.

In a particular embodiment, a mixed metal MOF of the disclosure can berepresented by the formula: (M¹)_(x)(M²)_(2-x)(dobdc, m-dobdc and/orH₄dotpdc^(R)), wherein at least one of M¹ or M² is redox-active metaland x is a number less than or equal to 1, 0.9, 0.8, 0.75, 0.7, 0.65,0.6, 0.55, 0.5, 0.45, 0.4, 0.35, 0.3, 0.25, 0.2, 0.15, 0.1, or 0.05. Ina particular embodiment, M¹ is selected from Fe, Mn, Co, Ni, and Cu, ora divalent cation of any of the foregoing. In another embodiment, M² isselected from Fe, Mn, Co, Ni, Cu, Be, Mg, Ca, Sr, Ba, Sc, Y, Ti, Zr, V,Nb, Ta, Cr, Mo, W, Re, Ru, Os, Rh, Ir, Pd, Pt, Ag, Au, Zn, Cd, Hg, Al,Ga, In, Si, Ge, Sn, Pb, As, Te, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Db, Tm,Yb, and La, or a divalent cation of any of the foregoing. In yet anotherembodiment, M² is selected from Mg, Ca, Sr, Ba, Sc, Y, Ti, Zr, V, Nb,Ta, Cr, Mo, W, Re, Ru, Os, Rh, Ir, Pd, Pt, Ag, Au, Zn, Cd, Hg, Al, Ga,In, Si, Ge, Sn, Pb, As, Te, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Db, Tm, Yb,and La, or a divalent cation of any of the foregoing. For example, for aMOF of the disclosure represented by the formula Fe_(x)Mg_(2-x)(dobdc),wherein x<0.3, catalyzed the oxidation of ethane so that only ethanoland acetaldehyde were generated. Further, a ratio of 25:1 of ethanol toacetaldehyde was generated when x=0.1. The MOFs of the disclosure havealso been shown to catalytically convert propane to propanol, andpropylene to propylene oxide in a highly selective manner. Further,other similar oxidations are possible when using MOFs which arecomprised of different redox-active and redox-inactive metals as well asusing m-dobdc instead of dobdc.

One of main advantages of the MOFs disclosed herein is high selectivelyfor converting hydrocarbons, (e.g., (C₁-C₆)-hydrocarbons) tocorresponding alcohols (e.g., (C₁-C₆)-alcohols) under mild conditionscan be achieved by using a cheap and abundant first-row transitionmetal(s). Moreover, de-activated MOFs (e.g., metal in an inactive 3+state instead of an active 2+ state) can be regenerated by treating theMOFs with a reducing agent, such as exposing the MOFs to 1,4-dienes(e.g., cyclohexadiene).

In a particular embodiment, a MOF of the disclosure can be used for avariety of applications, including for gas, liquid or vapor separation,gas storage, separation of bioproducts or compounds, or catalysis. Inparticular embodiment, the disclosure provides for MOFs that selectivelycatalyze the oxidations of one or more molecules. In a furtherembodiment, a MOF disclosed herein performs one or more of the followingcatalytic oxidations: oxidation of alkanes (such as (C₁-C₆) alkanes)into corresponding alcohols and/or aldehydes; catalyzes the oxidation ofclycohexane into KA oil (i.e., a mixture of cyclohexanol andcyclohexanone); catalyzes the oxidation of benzene to phenol; and theoxidation of alkenes to corresponding epoxides (e.g., propylene topropylene oxide, and ethylene to ethylene oxide).

The disclosure also provides an apparatus and method for catalyzing theoxidation of compounds having a feed side and an effluent side separatedby a MOF of the disclosure, wherein the one or more reactant(s) are fedon one side and the oxidized product(s) are generated as effluent. Theapparatus may comprise a column separation format, such as a heatedglass column, wherein the column may comprise the MOF.

In a particular embodiment, a MOF disclosed herein is part of a device.In a further embodiment, the device is a catalytic device whichcatalyzes the oxidation of light hydrocarbons (e.g., methane, ethane,and propane) into corresponding alcohols and/or aldehydes; catalyzes theoxidation of clycohexane into KA oil (i.e., a mixture of cyclohexanoland cyclohexanone); catalyzes the oxidation of benzene to phenol; andthe oxidation of alkenes to corresponding epoxides (e.g., propylene topropylene oxide, and ethylene to ethylene oxide).

The disclosure also provides methods using a MOF disclosed herein. In acertain embodiment, a method to catalytically oxidize one or morehydrocarbons using a MOF disclosed herein is provided.

A MOFs used in the embodiments of the disclosure include a plurality ofpores for catalysis. In one variation, the plurality of pores has aunimodal size distribution. In another variation, the plurality of poreshave a multimodal (e.g., bimodal) size distribution.

The following examples are intended to illustrate but not limit thedisclosure. While they are typical of those that might be used, otherprocedures known to those skilled in the art may alternatively be used.

Examples

General. Unless otherwise noted, all procedures were performed under anN₂ atmosphere using standard glove box or Schlenk techniques.N,N-dimethylformamide (DMF) was dried using a commercial solventpurification system designed by JC Meyer Solvent Systems and then storedover 4 Å molecular sieves. Anhydrous methanol was purchased fromcommercial vendors, further dried over 3 Å sieves for 24 hours, anddeoxygenated prior to being transferred to an inert atmosphere glovebox, where it was stored over 3 Å molecular sieves. The ethane, argon,and nitrous oxide used in reactivity studies were purchased at 99.999%,99.999%, and 99.998% purity, respectively. The 30% N₂O/N₂ mixture usedto synthesize Fe₂(OH)₂(dobdc) was purchased from commercial vendorsusing 99.5% purity N₂O and 99.999% purity N₂. All other reagents wereobtained from commercial vendors at reagent grade purity or higher andused without further purification. Carbon, hydrogen, and nitrogenanalyses were obtained from the Microanalytical Laboratory at theUniversity of California, Berkeley.

¹H-Nuclear Magnetic Resonance. ¹H-NMR spectra were obtained using aBruker AVB-400 instrument and peaks were referenced to residual solventpeaks.

Powder X-Ray Diffraction Data Collection and Refinement. X-raydiffraction data on Fe₂(OH)₂(dobdc) were collected on a Beamline 17-BM-Bat the Advanced Photon Source at Argonne National Laboratory (see FIGS.7 and 8). The sample was first heated in the presence of N₂O, from roomtemperature to 60° C. over the course of two days. Excess N₂O wasremoved, and the sample was pumped into an N₂ purged glove box where itwas loaded into a 1.0 mm borosilicate capillary. The capillary wasattached to a custom designed gas cell to maintain an inert atmosphere,and then brought out of the glove box. The cell was then attached to anoutgassing port on a Micromeritics ASAP 2020, where the remaining N₂ wasremoved and the sample was dosed with a small amount of Helium to serveas exchange gas. The capillary was then flame sealed for measurement. At17-BM the capillary was mounted onto the goniometer head and thencentered in the beam. Powder X-ray diffraction patterns (PXRD) wererecorded using a Bruker D8 Advance diffractometer (Göbel-mirrormonochromated Cu Kα radiation λ=1.54056 Å).

EXAFS Data Collection and Refinement.

X-ray absorption spectra (XAS) were collected at the Advanced LightSource (ALS) on beamline 10.3.2 with an electron energy of 1.9 GeV andan average current of 500 mA. The radiation was monochromatized by aSi(111) double-crystal monochromator. Intensity of the incident X-raywas monitored by an N₂-filled ion chamber (I₀) in front of the sample.Fluorescence spectra were recorded using a seven-element Ge solid-statedetector. The rising K-edge energy of Fe metal foil was calibrated at7111.20 eV.

Data reduction of the XAS spectra was performed using custom-madesoftware. Pre-edge and post-edge contributions were subtracted from theXAS spectra, and the results were normalized with respect to the edgejump. Background removal in k-space was achieved through a five-domaincubic spline. Curve fitting was performed with Artemis and IFEFFITsoftware using ab initio-calculated phases and amplitudes from theprogram FEFF.

Powder Neutron Diffraction Data Collection and Refinement.

Neutron powder diffraction (NPD) data (see FIGS. 9-12) were collected onthe high-resolution neutron powder diffractometer, BT1, at the NationalInstitute of Standards and Technology (NIST) Center for NeutronResearch. An activated sample of Fe₂(dobdc) (2.027 g) was placed insidea He-purged glove box and loaded into a vanadium sample can equippedwith a gas loading lid. The sample was then sealed inside of the canusing an indium o-ring and was then removed from the glove box andplaced on a bottom-loading closed cycle refrigerator. The sample wasfirst cooled to 10 K for data collection of the bare framework using aGe(311) monochromator (λ=2.0781 Å) and a 60 minute collimator.Fe₂(dobdc) was then warmed to room temperature where it was dosed withvarious predetermined amounts of N₂O gas, approximately 0.35, 0.60, and1.25 N₂O molecules per Fe²⁺ site. For each gas dosing the pressure wasfirst allowed to equilibrate over a ten minute period at roomtemperature, and then the sample was slowly cooled to 10 K over a periodof approximately 2.5 hours for data collection. Room-temperature neutronpowder diffraction data were collected on the high-resolution neutronpowder diffractometer, BT1, using a Ge(311) monochromator (λ=2.0781 Å)and a 60 minute collimator. All NPD data were analyzed using theRietveld method as implemented in EXPGUI/GSAS software package.

Mössbauer Spectroscopy.

Iron-57 Mbssbauer spectra were obtained at 295 K with a constantacceleration spectrometer and a cobalt-57 rhodium source. Prior tomeasurements the spectrometer was calibrated at 295 K with α-iron foil.Samples were prepared inside a N₂-filled glove box and contained 20mg/cm² of sample (7 mg/cm² of iron) diluted with boron nitride. Allspectra were fit with symmetric Lorentzian quadrupole doublets using theWMOSS Mbssbauer Spectral Analysis Software (wmoss.org).

Transmission and ATR Infrared Spectroscopy.

Attenuated total reflectance (ATR) infrared spectra were collected at 4cm⁻¹ resolution on a Perkin Elmer Avatar Spectrum 400 FTIR spectrometerequipped with a Pike attenuated total reflectance accessory. Theinstrument was placed inside an N₂-filled glove bag for measurement ofair-sensitive samples. In situ transmission FTIR spectra were collectedat 2 cm⁻¹ resolution on a Bruker Vertex 70 spectrophotometer equippedwith a DTGS detector. The materials were examined in the form ofself-supporting pellets (15-20 mg/cm²) mechanically protected with apure gold frame. Samples were inserted in a quartz IR cell, equippedwith KBr windows and characterized using a very small optical path. Thecell was attached to a conventional high vacuum glass line capable of aresidual pressure less than 10⁻⁴ mbar. This setting allowed both thermaltreatment and adsorption-desorption cycles of molecular probes in situ.All materials were prepared and inserted into the IR cell inside anN₂-filled glove box to avoid contact with oxygen and moisture.Fe₂(dobdc) samples were activated under dynamic vacuum (residualpressure <10⁻⁴ mbar) at 433 K for 18 h before being contacted withincreasing pressures of N₂O (up to 40 mbar).

Low-Pressure N₂ Isotherms.

For all gas adsorption measurements, 100-200 mg of sample weretransferred to a preweighed glass sample tube under an atmosphere ofnitrogen and capped with a Transeal. Samples were then transferred to aMicromeritics ASAP 2020 gas adsorption analyzer and heated at a rate of0.1 K/min from room temperature to a final temperature of 433 K and 483K for Fe₂(dobdc) and Fe_(0.1)Mg_(1.9)(dobdc), respectively. Samples ofFe₂(OH)₂(dobdc) were degassed at room temperature. Samples wereconsidered activated when the outgas rate at the degassing temperaturewas less than 2 pbar/min. Evacuated tubes containing degassed sampleswere then transferred to a balance and weighed to determine the mass ofsample. The tube was transferred to the analysis port of the instrumentwhere the outgas rate was again determined to be less than 2 pbar/min.Nitrogen gas adsorption isotherms at 77 K were measured in liquidnitrogen.

Calculations for Periodic Systems.

Starting from the experimental powder X-ray crystal structure, theperiodic structures for 2 and 4 were fully optimized using periodicdensity functional theory as implemented in the Vienna ab initiosimulation package (VASP) employing the generalized gradientapproximation exchange-correlation functional PBE. A Hubbard Ucorrection of 5 eV was added to the intra-site Coulomb interactions ofthe d-orbitals of the iron atoms to decrease the delocalization ofelectron density that results from the presence of the self-interactionof electrons in the PBE non-hybrid density functional. The VASPcalculations use projector-augmented wave potentials to describe theinteraction between core and valence electrons. A plane-wave kineticenergy cutoff of 610 eV was used and the integration over theirreducible Brillouin zone was carried out over a 3×3×3 k-points grid.Atomic positions were relaxed until the forces were lower than 0.06eV/A. All possible spin states were considered.

Cluster Calculations.

From the initial periodic structures of 2 and 4, we designed twocorresponding model clusters containing three neighboring metal centers(along a single helical chain) and their first coordination spheres.These clusters are analogous to the recently reported 88-atom clusterfor Fe₂(dobdc), which contained three pentacoordinate Fe(II) centers andsix organic linkers. As in the case of the 88-atom cluster model, thecluster model of 4 (containing 89 atoms, equivalent to the 88-atomcluster plus an additional O atom coordinated to the central Fe) and thecluster model of 2 (containing 90 atoms, equivalent to the 88-atomcluster plus an additional OH group coordinated to the central Fe) weredesigned to maintain an overall zero charge for the model system and topreserve a good representation of the first coordination sphere of thecentral iron atom from the periodic structure. The charge of the clusterwas set to zero by addition of protons was noted. The cluster modelswere simplified by substituting the two peripheral Fe(II) ions withZn(II) ions, while keeping only the central Fe ion in the cluster (notethat Fe(II) ions were not replaced by Zn(II) ions for the periodiccalculations).

Two-step constrained geometry optimizations were performed. In the firststep, the protons added to neutralize the cluster charge were optimized,while all the other atoms were kept in fixed positions. In the secondstep, only the central Fe and its first coordination sphere were allowedto relax. The first coordination sphere consists of the Fe atom, thefive O atoms of the bare MOF, and the atoms of the adsorbate (O, OH, orN₂O); since this involves optimizing six atoms of the bare MOF, it isdenoted “opt6”. All the optimizations were followed by frequencycalculations to confirm that the stationary point was a minimum, whichwas indicated by the absence of any imaginary frequency in the optimizeddegrees of freedom.

All density functional cluster calculations used the Gaussian 09software package or a locally modified version of Gaussian 09. The PBE,M06-L, M06, M08-SO, MPW1B95, and PW6B95 exchange-correlation functionalswere employed. For the Minnesota density functionals (M06-L, M06,M08-SO, MPW1B95, and PW6B95), an ultrafine grid (99 radial nodes and 590angular nodes) was used to perform numerical integrations. Thestable=opt keyword of Gaussian was used to test the stability of theKohn-Sham Slater determinant and converge to a stable solution. Anautomatic density-fitting set generated by the Gaussian program was usedto reduce the cost for calculations done with the local densityfunctionals, PBE and M06-L. The 6-31G(d) basis set was used for H, C, N,O, and Mg while the Stuttgart [8s7p6d1f|6s5p3d1f] ECP10MDF contractedeffective core potential basis set was employed for Fe and Zn.Single-point calculations were performed with the 6-311+G(2df,p) basisset for H, C, and O and the Stuttgart [8s7p6d1f 6s5p3d1f] ECP10MDFcontracted effective core potential basis set for Fe and Zn. These basissets have been previously successfully employed in the study ofmolecular systems with similar M=O and M-OH motifs.

Multi-Reference Calculations.

Single-point multiconfigurational complete active space (CASSCF)calculations followed by second-order perturbation theory (CASPT2) wereperformed at the DFT-optimized (PBE/SDD(Fe, Zn), 6-31G(d) (C, H, O))geometries of the cluster models of 2 and 4. These calculations wereperformed with the Molcas 7.8 software package. Scalar relativisticeffects were included by use of the second order Douglas-Kroll-HessHamiltonian. The computational cost arising from the two-electronintegrals was reduced by employing the Cholesky decomposition technique(RICD). The relativistic all-electron ANO-RCC basis sets were used forall atoms; in particular, the ANO-RCC-VTZP basis set was used for Fe,for the five first-coordination-sphere O atoms of Fe in the MOFfragment, and for the O or OH atoms of the adsorbate. ANO-RCC-VDZP wasused for the Zn and all other O atoms, and ANO-RCC-MB was used for all Cand H atoms. No symmetry (point group C₁) was used, and all possiblespin states were considered. The default IPEA shift of 0.25 eV was usedin CASPT2, along with an imaginary shift of 0.2 eV.

An active space containing 10 electrons in 11 orbitals (10,11) was usedfor the cluster model of 4. An active space containing 5 electrons in 5orbitals (5,5), which contains the five d electrons of Fe(III) in thefive 3d orbital was used for the cluster model of 2. The sigma bondingorbital of the metal to the —OH ligand is doubly occupied in theinactive space, along with the five other Fe—O sigma bonding orbitals.

Synthesis of Fe₂(OH)_(0.6)(dobdc) and Fe₂(OH)₂(dobdc).

Fe₂(dobdc) was synthesized according to Bloch et al. (J. Am. Chem. Soc.133, 14814-14822 (2011)). An evacuated schlenk flask containing fullydesolvated Fe₂(dobdc) (100 mg, 0.33 mmol) was placed under an atmosphereof 30% N₂O and 70% N₂. The flask was immersed in an oil bath, and thetemperature was increased by 10° C. every 12 hours, from 25° C. up to60° C., to obtain Fe₂(OH)₂(dobdc) as a dark red-brown solid. If thereaction is stopped after 12 hours at 35° C., the partially oxidizedFe₂(OH)_(0.6)(dobdc) (as determined by Mössbauer) is obtained. Anal.Calc. for C₈H₄Fe₂O₈: C, 28.28; H, 1.19. Found: C, 29.18; H, 1.16. IR(solid-ATR): 3679 (m), 1532 (s), 1450 (s), 1411 (s), 1361 (s), 1261 (s),1154 (w), 1129 (w), 1077 (w), 909 (m), 889 (s), 818 (s), 807 (s), 667(s), 630 (m), 594 (s), 507 (s).

Synthesis of Fe₂(¹⁸OH)_(0.6)(dobdc).

Dried ¹⁸O-labeled ammonium nitrate (50 mg, 0.58 mmol) was placed in astainless steel reactor equipped with a two-way valve connected to ahose adapter. The reactor was evacuated and refilled with N₂ (3×) andthen heated, closed, to 200° C. After 24 hours, the reactor was cooledto 0° C., and the evolved N₂ ¹⁸O was carefully condensed into anevacuated schlenk flask cooled to 77 K containing Fe₂(dobdc) (15 mg,0.05 mmol). The sample was allowed to react for 12 hours at 35° C.,after which the partially oxidized sample was analyzed by IR.

Synthesis of Fe_(0.1)Mg_(1.9)(dobdc).

In a 500 mL schlenk flask, H₄(dobdc) (1.75 g, 8.8 mmol), MgCl₂ (1.47 g,15.4 mmol), and FeCl₂ (0.84 g, 6.6 mmol) were dissolved in DMF (310 mL)and MeOH (40 mL). The reaction was stirred vigorously at 120° C. for 16hours. The precipitate was filtered and stirred in fresh DMF (250 mL) at120° C. for three hours. Two more DMF washes at 120° C. were performed,after which the precipitate was filtered and soaked in methanol at 60°C. The methanol exchanges were repeated until no DMF stretches werevisible by IR. The framework was fully desolvated under dynamic vacuum(<15 μbar) at 210° C. for 2 days to afford Fe_(0.1)Mg_(1.9) (dobdc) as abright yellow-green solid (2.02 g, 8.2 mmol, 93% yield).Fe_(0.44)Mg_(1.56)(dobdc) and other analogs with different Fe:Mg ratioscan be obtained by simply varying the ratio of MgCl₂ and FeCl₂ whilekeeping all other synthetic conditions the same. The iron to magnesiumratio was determined by ICP-OES. Anal. Calc. for C₈H₂Fe_(0.1)Mg_(1.9)O₆:C, 39.08; H, 0.82. Found: C, 39.37; H, 0.43. IR (solid-ATR): 1577 (s),1484 (m), 1444 (s), 1429 (s), 1372 (s), 1236 (s), 1210 (s), 1123 (m),911 (m), 892 (s), 828 (s), 820 (s), 631 (s), 584 (s), 492 (s).

Synthesis of Fe₂(Dobpdc) and Other Expanded Analogues:

Fe₂(dobpdc) (dobpdc⁴⁻=4,4′-dioxidobiphenyl-3,3′-dicarboxylate) can besynthesized by combining 2.5 equivalents of FeCl₂ with 1 equivalent ofligand in a mixture of DMF:MeOH (8:2) at 120° C. for 18 hours; thethree-ring frameworks can be synthesized in a similar manner. Aftermethanol exchanges, the frameworks can be fully desolvated upon heatingto 250° C. under dynamic vacuum to generate exposed Fe^(II) sites. Themixed Fe/Mg frameworks can be synthesized by using a mixture of FeCl₂and MgCl₂ for a total of 2.5 equivalents of metal per equivalent ofligand.

Synthesis of Fe₂(Dotpdc) and Other Expanded Analogues:

Fe₂(dotpdc)(H₄dotpdc=4,4″-dihydroxy-[1,1′:4′,1″-terphenyl]-3,3″-dicarboxylic acid:

can be synthesized by combining 2.5 equivalents of FeCl₂ with 1equivalent of ligand in a mixture of DMF:MeOH (9:1) at 140° C. for 48hours. After methanol exchanges, the framework can be fully desolvatedupon heating to 180° C. under dynamic vacuum to generate exposed Fe^(II)sites. Frameworks containing the other ligand derivatives (R=H, CH₃, F,and tBu):

can be synthesized in a similar manner.

PXRD characterization and Rietveld Analysis of Fe_(x)Mg_(2-x)(dobdc)frameworks: Data was first collected at room temperature using a Si(111) monochromator (λ=0.7291 Å, ΔE/E=1.5*10⁻⁴) and then again after thesample was cooled at a rate of 2 K/min to 100 K in an N₂ cryostream. Itshould be noted that the sample was held at 100 K for 30 minutes priorto data measurement to allow for temperature equilibration. Rietveldanalysis was carried out on both data sets in order to elucidate thesite positions of the OH groups on the Fe³⁺ centers. Results of Rietveldanalysis obtained from X-ray diffraction experiments of Fe₂(OH)₂(dobdc)can be seen in TABLE 1 and TABLE 2:

TABLE 1 Rietveld Refinement (100K.) of Fe₂ (OH)₂(dobdc). Space groupR-3, a = 25.6125(2) Å, c = 6.8036(1) Å, and V = 3865.20(8) Å³. This datawas obtained from 11-BM at the Advanced photon source at ArgonneNational Laboratory using a wavelength of 0.7291 Å. Uiso*100 Atom x y zocc. (Å²) Fe 0.3893(1) 0.3510(1)    0.1539(3) 1.0 2.95* O1 0.3230(3)0.2972(4)   0.356(1) 1.0 2.3(2) O2 0.3009(4) 0.2289(3)   0.594(1) 1.02.3(2) O3 0.3553(3) 0.2727(4)   0.000(1) 1.0 2.3(2) C1 0.3164(8)0.2467(6)   0.415(2) 1.0 1.1(2) C2 0.3260(6) 0.2052(7)   0.288(2) 1.01.1(2) C3 0.3431(5) 0.2202(7)   0.092(2) 1.0 1.1(2) C4 0.3492(6)0.1795(7) −0.044(2) 1.0 0.9(2) OH 0.4524(4) 0.3473(5)   0.294(1) 1.08.66* *Uaniso Fe = [U₁₁, U₂₂, U₃₃, U₁₂, U₁₃, U₂₃] = [4.0(2), 1.9(2),1.7(1), 0.5(2), 0.4(2), 0.4(2)]; Uaniso Ox = [U₁₁, U₂₂, U₃₃, U₁₂, U₁₃,U₂₃] = [7(1), 15(1), 8(1), 10(1), 0.00, 0.00]

TABLE 2 Rietveld Refinement (298K) of the Fe₂(OH)₂(dobdc). Space groupR-3, a = 25.6191(2) Å, c = 6.8042(1) Å, and V = 3867.55(9) Å³ Uiso*100Atom x y z occ. (Å²) Fe 0.3897(1) 0.3512(1)   0.1540(4) 1.0  3.14* O10.3222(4) 0.2967(4)   0.358(1) 1.0  2.6(2) O2 0.3005(4) 0.2295(4)  0.596(1) 1.0  2.6(2) O3 0.3553(4) 0.2736(4) −0.004(2) 1.0  2.6(2) C10.3167(8) 0.2473(7)   0.416(2) 1.0  1.6(2) C2 0.3265(6) 0.2051(7)  0.294(2) 1.0  1.6(2) C3 0.3431(6) 0.2219(7)   0.101(2) 1.0  1.6(2) C40.3488(6) 0.1815(7) −0.039(2) 1.0  1.6(2) Ox 0.4528(5) 0.3489(6)  0.297(1) 1.0 12.2* *Uaniso Fe = [U₁₁, U₂₂, U₃₃, U₁₂, U₁₃, U₂₃] =[4.4(2), 1.8(2), 1.5(1), 0.3(2), 0.5(2), −0.3(2)]; Uaniso Ox = [U₁₁,U₂₂, U₃₃, U₁₂, U₁₃, U₂₃] = [8(1), 27(2), 9(1), 14(1), 0.00, 0.00]

For the unit cell determination of Fe_(x)Mg_(2-x)(dobdc), amicrocrystalline sample of the material was gently ground and loadedinto a 1.0 mm borosilicate capillary inside an N₂-filled glove box. Thesample was sealed temporarily with silicone grease before it was takenout of the box and flame-sealed. Diffraction data were collected duringan overnight scan in the 2θ range of 4-65° with 0.020 steps using aBruker AXS D8 Advance diffractometer equipped with CuKα radiation(λ=1.5418 Å), a Lynxeye linear position-sensitive detector, and mountingthe following optics: Göbel mirror, fixed divergence slit (0.6 mm),receiving slit (3 mm), and secondary beam Soller slits (2.5°). Thegenerator was set at 40 kV and 40 mA. A standard peak search, followedby indexing via the Single Value Decomposition approach, as implementedin TOPAS-Academic, allowed the determination of approximate unit celldimensions. Precise unit cell dimensions were determined by performing astructureless Le Bail refinement in TOPAS-Academic.

Neutron Fourier Difference Analysis of Fe₂(Dobdc).

Neutron Fourier difference analysis of the bare Fe₂(dobdc) frameworkrevealed no excess scattering density in the channel indicating that thesample was sufficiently activated. The structural model of the activatedmaterial was refined with all structural and peak profile parametersfree to vary, resulting in a structure very similar to that previouslydetermined (see TABLE 3).

TABLE 3 Rietveld Refinement (10K) of Fe₂(dobdc). Fractional atomiccoordinates, occupancies, and isotropic displacement parameters obtainedfrom Rietveld refinement of structural model of the bare Fe₂(dobdc)framework at 10K, space group R-3, a = 26.1826(6) Å, c = 6.8506(2) Å ,and V = 4067.1(2) Å³. Uiso*100 Atom x y z occ. (Å²) Fe 0.3815(2)0.3518(2)   0.1416(5) 1.0 0.4(1) O1 0.3293(3) 0.2963(3)   0.369(1) 1.00.4(1) O2 0.3001(3) 0.2259(3)   0.600(1) 1.0 0.4(1) O3 0.3550(3)0.2737(3)   0.011(1) 1.0 0.4(1) C1 0.3189(3) 0.2453(3)   0.4267(9) 1.00.51(6) C2 0.3278(3) 0.2063(3)   0.2915(8) 1.0 0.51(6) C3 0.3441(3)0.2221(3)   0.0908(8) 1.0 0.51(6) C4 0.3490(3) 0.1809(3) −0.030(1) 1.00.51(6) H 0.3621(5) 0.1922(5) −0.173(2) 1.0 1.8(3)

Once completed, the same procedure was carried out for data obtainedfrom the sample loaded with gas revealing both the site positions andorientations of framework bound N₂O (see TABLES 4-6).

TABLE 4 Rietveld Refinement (10K) of Fe₂(dobdc) (N₂O)_(0.7). Fractionalatomic coordinates, occupancies, and isotropic displacement parametersobtained from Rietveld refinement of structural model of the 0.35 N₂Oper Fe²⁺ in the Fe₂(dobdc) framework at 10K, space group R-3, a =26.1660(4) Å, c = 6.8595(2) Å, and V = 4067.2(2) Å³. Uiso*100 Atom x y zocc. (Å²) Fe 0.3819(1) 0.3520(2)   0.1437(4) 1.0 0.49(5) O1 0.3279(2)0.2957(2)   0.3676(8) 1.0 0.20(4) O2 0.3010(2) 0.2272(2)   0.6019(7) 1.00.20(4) O3 0.3550(2) 0.2738(2)   0.0084(8) 1.0 0.20(4) C1 0.3193(2)0.2463(2)   0.4292(7) 1.0 0.42(2) C2 0.3275(2) 0.2063(2)   0.2887(7) 1.00.42(2) C3 0.3438(2) 0.2213(2)   0.0924(7) 1.0 0.42(2) C4 0.35061(2)0.1817(2) −0.0272(7) 1.0 0.42(2) H 0.3619(4) 0.1930(3) −0.1712(15) 1.01.3(2) O11 0.471(1) 0.358(1)   0.272(4) 0.22(1) 1.6(8) N12 0.5174(5)0.3960(4)   0.2071(17) 0.371(7) 2.9(3) N13 0.5607(6) 0.4314(6)  0.1533(26) 0.223(6) 1.6(4) N11a 0.4718(9) 0.3605(9)   0.2628(32)0.161(7) 1.1(6) O13a 0.562(2) 0.433(2)   0.146(7) 0.16(1) 3(1)

TABLE 5 Rietveld Refinement (10K) of Fe₂(dobdc) (N₂O)_(1.2). Fractionalatomic coordinates, occupancies, and isotropic displacement parametersobtained from Rietveld refinement of structural model of the 0.60 N₂Oper Fe²⁺ in the Fe₂(dobdc) framework at 10K, space group R-3, a =26.1577(4) Å, c = 6.8671(2) Å, and V = 4069.1(2) Å³. Uiso*100 Atom x y zocc. (Å²) Fe 0.3829(1) 0.3523(2)   0.1428(5) 1.0 0.94(5) O1 0.3268(2)0.2945(2)   0.3667(8) 1.0 0.17(4) O2 0.3019(2) 0.2274(2)   0.6000(7) 1.00.17(4) O3 0.3550(2) 0.2733(2)   0.0093(8) 1.0 0.17(4) C1 0.3189(2)0.2452(2)   0.4273(7) 1.0 0.86(2) C2 0.3280(2) 0.2059(2)   0.2857(7) 1.00.86(2) C3 0.3446(2) 0.2211(2)   0.0933(7) 1.0 0.86(2) C4 0.3521(2)0.1833(2) −0.0262(7) 1.0 0.86(2) H 0.3602(3) 0.1927(3) −0.170(1) 1.01.0(2) O11 0.468(1) 0.3533(9)   0.272(3) 0.232(5) 1.5(7) N12 0.5145(4)0.3915(4)   0.211(2) 0.532(7) 7.9(4) N13 0.5575(8) 0.4275(8)   0.152(4)0.232(5) 6.8(7) N11a 0.4712(6) 0.3560(6)   0.264(2) 0.310(6) 5.5(5) O13a0.5599(8) 0.4296(8)   0.151(3) 0.310(6) 3.3(6)

TABLE 6 Rietveld Refinement (10K) of Fe₂(dobdc) (N₂O)_(2.5). Fractionalatomic coordinates, occupancies, and isotropic displacement parametersobtained from Rietveld refinement (10K) of the Fe₂(dobdc) dosed with1.25 N₂O per Fe²⁺, space group R-3, a = 26.1243(5) Å, c = 6.87522(2) Å,and V = 4063.6(2) Å³. Uiso*100 Atom x y z occ. (Å²) Fe 0.3828(2)0.3518(2)   0.1479(6) 1.0  0.95(9) O1 0.3271(3) 0.2952(3)   0.3619(9)1.0  0.32(7) O2 0.3006(3) 0.2252(3)   0.593(1) 1.0  0.32(7) O3 0.3554(3)0.2736(3)   0.006(1) 1.0  0.32(7) C1 0.3194(2) 0.2471(3)   0.4234(9) 1.0 0.81(4) C2 0.3267(3) 0.2057(3)   0.2872(8) 1.0  0.81(4) C3 0.3457(2)0.2223(3)   0.0956(9) 1.0  0.81(4) C4 0.3507(3) 0.1808(3) −0.0232(9) 1.0 0.81(4) H 0.3632(5) 0.1931(4) −0.169(2) 1.0  1.35(3) O11 0.4704(7)0.3515(9)   0.249(4) 0.320(8)  3.7(9) N12 0.5176(3) 0.3919(3)   0.213(1)0.639(9)  5.4(4) N13 0.5610(5) 0.4309(7)   0.164(3) 0.320(8)  4.9(6)N11a 0.4711(5) 0.3630(7)   0.268(2) 0.308(8)  1.4(4) N13a 0.5657(6)0.4187(16)   0.142(4) 0.308(8) 10.4(8) N21 0.1468(8) 0.1587(8)  0.605(3) 0.383(5) 10.0(8) N22 0.1620(7) 0.1862(7)   0.462(3) 0.383(5) 8.0(7) O23 0.1744(1) 0.2166(9)   0.331(3) 0.383(5)  3.8(7) N11aa0.5090(6) 0.3732(7)   0.333(2) 0.310(5)  2.4(5) O11aa 0.559(1) 0.403(1)  0.402(4) 0.310(5)  0.7(6) N11ab 0.4619(8) 0.3481(8)   0.285(3)0.310(5)  3.7(6)

Unlike X-rays, neutrons are scattered from the nucleus allowingneighboring atoms with similar electron densities to exhibit nonlinearvariations in scattering power. Nitrogen and oxygen have coherentscattering lengths of 9.36 fm and 5.80 fm, respectively. This impliesthat neutrons should be very sensitive to the atomic assignment of O andN, an especially important feature when considering the large esdsassociated with bond distances determined from position averaged powderdata. Fourier Difference Analysis of the data obtained from the sampleloaded with 0.35 N₂O per Fe²⁺ reveals that the N₂O binds in an end-onfashion with a distance of approximately 2.40(2) A from the Fe²⁺ and isangled with respect to the framework surface at 118(2)° (see FIG. 13).For assignment of the atoms responsible for binding to the metal site,both Fe²⁺—O and Fe²⁺—N binding were tried. First, the occupancies of theN—N—O atoms were constrained to be equal. Once a stable refinement wasachieved, the occupancies of the individual atoms in the N₂O moleculewere allowed to vary independently of one another. In either case of M-Oor M-N binding, the occupancies of both terminal N₂O atoms deviatedsignificantly from the average value and lead to an improvement in theoverall refinement. The observed increase and/or decrease in theoccupancies correlated with our expectations based on the knowndifferences in scattering lengths of the O and N. The results imply thatpure O or N coordination at the metal site was incorrect. Further, thestructural model showed only average distances for both N—N and N—O,around 1.15 Å, and so a clear assignment of the binding mechanism of theN₂O could not be made purely through assessment of bond distances.Considering all of these factors, the refinement with mixed O and Nbinding for the N₂O molecules were performed revealing an average ofapproximately 60% O and 40% N at the open metal site. The intramolecularN₂O angle was refined at a value of 178(2)°, which, within error of theneutron diffraction experiment, did not deviate from the expected lineargeometry.

At higher loadings (0.6 and 1.25 equivalents of N₂O), disorder at themetal and the presence of multiple binding sites prevented accuratedetermination of the binding mode (see FIG. 14). In particular, uponincreasing the N₂O loading to 0.6 and then 1.25 N₂O per Fe^(2+,) therewas further population of the site I molecule and then the subsequentintroduction of a secondary adsorption site. Population of binding siteII appeared to induce a rearrangement of the site I molecule, referredto from this point forward as site Ia (see FIG. 14). While the data wasnot good enough to distinguish the binding mechanism in these twodifferent orientations, a significant change in the angle of the N₂Owith respect to the framework surface was seen, which changes from ˜120°to ˜145°. Intermolecular distances between site I and II, on the orderof 2.2 Å, are significantly shorter than the sum of the van der Waalsradii for N (1.55 Å) and/or O (1.52 Å). As a result, this interactionwas expected to be quite unfavorable. Further, the refined occupanciesof site II, ˜34%, and site I, ˜68%, support the idea that the two sitesare never simultaneously occupied.

In situ transmission-mode FTIR charcterization of Fe₂(dobdc). Contactwith 40 mbar of N₂O causes the appearance of extremely strong bands inthe 2280-2160 cm⁻¹ spectral range, associated with ν(N—N) of N₂O, whilethe rest of the IR spectrum was substantially unaffected (see FIG. 15A).Dominant absorptions due to the framework modes below 1600 cm⁻¹ do notallow the monitoring of the ν(N—O) band in N₂O, which was expected to bearound 1286 cm⁻¹. The spectrum profile verified the formation of acondensed phase inside the Fe₂(dobdc) channels, as the ν(N—N) band doesnot present the expected profile of a free linear rotator (P and Rbranches with the lack of the pure vibrational transition, Q branch).

FIG. 15B illustrates in detail the spectral range due to ν(N—N) band(spectra reported after background subtraction). The spectrum at highestcoverage (blue curve) was characterized by a very intense band,ascribable to the ν(N—N) in N₂O molecule, behaving as an hinderedrotator. The maximum was observed at 2226 cm⁻¹, a position very close tothat expected for the fundamental transition of pure N₂O molecule (2224cm⁻¹). The very small blue shift with respect to the position of N₂O gasindicated that N₂O interacts weakly with the Fe(II) species, giving riseto a physically adsorbed (liquid-like) phase. The main peak wasaccompanied by further components at higher (clear maximum at 2240 cm⁻¹)and lower (broad features at 2220, 2214 and 2206 cm⁻¹) frequencies,suggesting that, at the measuring temperature (beam temperature), N₂Omolecules may still partially retain their roto-vibrational profile(compare the spectra with that obtained in case of gaseous N₂O, bluedotted spectrum).

In case of Fe-silicalite the appearance of a doublet at 2282 cm⁻¹ and at2248 cm⁻¹ was assigned to the formation of two slightly different Fe—N₂Oadducts, while a component at 2226 cm⁻¹ was associated to the formationof weaker adducts with Brønsted sites. In the present case similarassignments were discarded, as all the above-mentioned signalsdisappeared at the same rate upon outgassing at room temperature (seelight grey spectra in FIG. 15B). The total reversibility of thesecomponents further confirmed the weak nature of the interaction of N₂Owith the Fe(II) sites in Fe₂(dobdc) sample.

Prolonged heating in N₂O at 60° C. gave rise to a spectrum characterizedby a strong band at 3678 cm⁻¹ and by a clear component at 670 cm⁻¹. Thepeak at 3678 cm⁻¹ can be associated to a ν(O—H) specie and the componentat 670 cm⁻¹ can be ascribed to a ν(Fe—OH) specie. The formation of thesehydroxide species was associated with the reactivity of N₂O, asindicated by the decrease in intensity for the adsorbed N₂O band (seeFIG. 16A).

Cyclohexadiene Reactivity of Fe₂(OH)_(0.6)(dobdc). Neat cyclohexadiene(160 mg, 2.0 mmol) was added to Fe₂(OH)_(0.6)(dobdc) (66 mg, 0.125 mmolFe(III), determined by Mössbauer) and allowed to react for 24 hours,during which a visible color change from red-brown to light yellow wasobserved. The sample was then extracted with CD₃CN (3×1 mL), and theproducts analyzed by 1H NMR using 1,2,4,5-tetramethylbenzene as aninternal standard. Benzene as the sole product was obtained inquantitative yield.

Reactivity of Fe₂(dobdc) and Fe_(0.1)Mg_(1.9)(dobdc) with N₂O and C₂H₆.

In a typical flow-through experiment, a mixture of gases (2 mL/min N₂O,10 mL/min C₂H₆, and 8 mL/min Ar for a total flow 20 mL/min) was flowedover a packed bed of metal-organic framework (50 to 100 mg) containedwithin a glass column. The column was heated to 75° C. for twenty-fourhours, after which the products were extracted with CD₃CN (3×1 mL) andanalyzed by 1H NMR using 1,4-dichlorobenzene as an internal standard.While a cold bath maintained at −78° C. was installed downstream of theglass reactor in order to collect condensable organic products, at thetemperatures tested all the products appear to remain bound to theframework. Yield for Fe_(0.1)Mg_(1.9)(dobdc): 9.5:1ethanol:acetaldehyde, 60% yield based on Fe.

In a typical batch experiment, a Parr bomb was charged with 50-100 mg ofFe_(0.1)Mg_(1.9)(dobdc), N₂O (1.5 bar), and C₂H₆ (7.5 bar) and heated to75° C. in a sand bath. After twenty-four hours, the bomb was cooled andthe products extracted with CD₃CN. Yield for Fe_(0.1)Mg_(1.9)(dobdc):25:1 ethanol:acetaldehyde, 1.6 turnovers based on Fe. In a typicalexperiment, this corresponds to functionalization of roughly 1% of theethane molecules.

Reactivity of Fe₂(Dobpdc) with N₂O and Ethane:

Heating Fe_(0.25)Mg_(1.75) (dobpdc) in a bomb with 1.5 bar of N₂O and8.5 bar of ethane at 75° C. results in a 13:1 mixture ofethanol:acetaldehyde. The overall yield is ˜70% with respect to iron,due to catalyst decomposition into an inactive Fe(III) phase.

Reactivity of Fe₂(Dobpdc) with Cyclohexane and Iodosylarene:

At room temperature, 1 equiv. of Fe₂(dobpdc) was combined with 2 equiv.of the oxidant 2-(tert-butylsulfonyl)iodosylbenzene and 20 equiv. ofcyclohexane in CD₃CN. Analysis of the products shows that cyclohexanoland cyclohexanone were produced in a 1.2:1 ratio.

Reactivity of Fe₂(Dotpdc) with Cyclohexane and Iodosylarene:

At room temperature, 1 equiv. of Fe₂(dotpdc^(R)) was combined with 5 to20 equiv. of the oxidant 2-(tert-butylsulfonyl)iodosylbenzene and 150equiv. of cyclohexane in CD₃CN (see FIG. 29a ). After 1.5 hours,analysis of the products shows that exclusively cyclohexanol andcyclohexanone were produced, in nearly quantitative yields based onoxidant. The alcohol:ketone (A:K) ratios depended on the identity of theorganic ligand (see FIG. 29b ). It was found that more hydrophobic,alkyl-containing ligand substituents led to higher A:K ratios. Solution-and gas-phase studies suggest the ligand substituents alter the poreenvironment and help modulate the cyclohexane concentration inside thepore. Briefly, alkyl substituents interact more favorably withcyclohexane, leading to higher local cyclohexane concentrations andgreater A:K selectivities. This can be potentially extended fromcyclohexane to other hydrocarbons.

Control Experiments.

No products were observed if N₂O, ethane, or Fe₂(dobdc)/Fe_(0.1)Mg_(1.9)(dobdc) was removed from the reaction mixture. The same flow-through andbatch experiments performed on Mg₂(dobdc) led to no observed products.The same conditions applied to Fe₂(dobdc) diluted in Mg₂(dobdc) did notlead to a clean reaction (unlike Fe_(0.1)Mg_(1.9) (dobdc)). Finally, anautoxidation process was ruled out by repeating the batch experimentwith added O₂ (1 bar), N₂O (1.5 bar), and C₂H₆ (7.5 bar). The yield wassignificantly lower (11% based on iron) and the ethanol selectivity muchworse (1:2.67 ethanol:acetaldehyde), indicating that the reportedreactivity is not due to autoxidation.

Analyzing the Reversible Binding of N2O to Fe₂(dobdc).

The binding of nitrous oxide to 1 under conditions in which the Fe—N₂Ointeraction is reversible was first investigated. Experimental studieson the coordination chemistry of N₂O are scarce, as metal-N₂O adductsare challenging to synthesize due to the poor σ-donating and π-acceptingproperties of the molecule. Indeed, of the several proposed bindingmodes, only one-end-on, η¹-N-has been structurally characterized in amolecular complex. To establish the coordination mode of N₂O in 1,powder neutron diffraction data, which are very sensitive to the atomicassignment of O and N, were collected on a sample dosed with variousloadings of N₂O. At low loadings, the best fit was an average ofapproximately 60% η¹-O and 40% η¹-N coordination, with Fe—N₂O distancesof 2.42(3) and 2.39(3) A, respectively. In both cases, a bent Fe—N₂Oangle close to 120° was observed (see FIG. 3B). Density functionaltheory (DFT) studies of N₂O-bound 1 using the M06 functional showexcellent agreement with experimental (see FIG. 4A-B). Furthermore,these calculations predict the η¹-O coordination mode to be favored overthe η¹-N mode by just 1.1 kJ/mol (see TABLES 7 and 8). This isconsistent with the nearly equal population split observed, although themagnitude of the difference is smaller than the reliability of thecalculations.

TABLE 7 Calculated relative energies (kJ/mol) for N₂O bound to theFe(II) site of the 88-atom cluster. The relative energies of η¹-N andη¹-O coordination modes are computed using M06-L and M06 densityfunctionals with the def2-TZVP and SDD(Fe, Zn), 6-31G(d) (C, H, O, N)basis sets. The level of optimization is opt6. Functional SDD (Fe, Zn),6-31G(d) mode Binding (C, H, O, N) def2-TZVP M06-L η¹-O 0.0 0.0 η¹-N−4.6 −9.5 M06 η¹-O 0.0 0.0 η¹-N 1.1 −4.5

TABLE 8 Binding energies^(a) (kJ/mol) of η¹-N and η¹-O coordinationmodes of N₂O bound to the iron(II) site of the 88-atom cluster. Thecalculations were done using M06-L and M06 density functionals withSDD(Fe, Zn), 6-31G(d) (C, H, O, N) basis set. The level of optimizationis opt6. Binding Binding energy Functional mode (kJ/mol) M06-L η¹-O 41.4η¹-N 46.1 M06 η¹-O 45.6 η¹-N 44.5 ^(a)Binding Energy = E(cluster) +E(N₂O) − E(complex)

While η¹-O coordination with a bent Fe—O—N angle has been proposed in avariety of systems ranging from isolated metal atoms to iron zeolites,η¹-N coordination with a bent Fe—N—N angle is much more unusual. Itsuggests little n-back-bonding from the metal d-orbitals into the π* ofN₂O, in contrast to previously reported vanadium and ruthenium-N₂Oadducts, which have linear metal-N—N—O geometries and for whichn-interactions have been postulated as significant contributors to thestability of the complexes. The bent geometry, long Fe—N₂O bond length,and mixed N- and O-coordination indicate N₂O was bound only weakly tothe iron(II) centers in the framework, a hypothesis corroborated byin-situ transmission-mode infrared spectroscopy. Spectra collected on athin-film of 1 dosed at room temperature with N₂O displayed a maximum at2226 cm⁻¹, which was very close to the fundamental ν(N—N) transition forunbound N₂O (2224 cm⁻¹), suggesting a physically adsorbed phase withlittle to no perturbation of the N₂O molecule (see FIG. 15A-B). Asexpected, this interaction is fully reversible, and the band completelydisappears under applied vacuum. Consistent with these experimentalresults, DFT studies calculate binding energies of 45.6 and 44.5 kJ/molfor the η¹-O and η¹-N modes, respectively, with a natural bond orderanalysis showing weak back-bonding in both configurations (see TABLE 9).

TABLE 9 Natural bond analysis of η¹-N and η¹-O coordination modes of N₂Obound to the iron(II) site of the 88-atom cluster. Binding mode %Back-bonding η¹-O 42% η¹-N 43%

Upon heating the N₂O-dosed framework to 60° C., the material underwent adrastic color change from bright green to dark red-brown that wassuggestive of oxidization. In addition, in situ infrared studies usingCO as a probe molecule showed that the open metal sites, whichcoordinate CO strongly, had been almost entirely consumed (see FIG.17A-B). Characterization of the resulting product was consistent withthe formation of Fe₂(OH)₂(dobdc) (2), in which each iron center is inthe +3 oxidation state and bound to a terminal hydroxide anion (see FIG.18A). Compound 2 was likely formed via a fleeting iron-oxo intermediate,which rapidly underwent H-atom abstraction, although the source of theH-atom has not been yet determined. Mössbauer spectroscopy was used toprobe the local environment of the iron centers in the oxidizedmaterial. The ⁵⁷Fe Mössbauer spectrum of 2 consists of a doubletcharacterized by an isomer shift (5) of 0.40(2) mm/s and a quadrupolesplitting (IAEQI) of 0.96(1) mm/s (see FIG. 18B). The isomer shift forthe iron centers in 2 is similar to the parameters obtained for theperoxide-coordinated iron(III) centers in Fe₂(O₂) (dobdc), and isconsistent with other high-spin heme and nonheme iron(III) species. Inaddition, the infrared spectrum of 2 showed the appearance of two newbands as compared to the unoxidized framework, which was assigned asFe—OH (667 cm⁻¹) and O—H (3678 cm⁻¹) vibrations. These bands shift to639 and 3668 cm⁻¹, respectively, when N₂₁₈O is employed for theoxidation; the observed differences of 28 and 10 cm⁻¹ were very close tothe theoretical isotopic shifts of 27 and 12 cm⁻¹ predicted by a simpleharmonic oscillator model (see FIG. 20A). Partial oxidation of theframework was achieved by heating at 35° C. for 12 h, leading to theformation of Fe₂(OH)_(0.6)(dobdc) (2′), which has a similar infraredspectrum (though the bands associated with Fe—OH are less intense) andMössbauer parameters (see TABLE 10).

TABLE 10 Mössbauer spectral parameters. |ΔΕ_(Ω)| Area Sample δ, mm/smm/s Γ, mm/s (%) Assignment Fe₂(OH)₂(dobdc) 0.40(2) 0.96(1) 0.34(1) 80(2) Fe^(III—)OH (1) 0.40(2) 1.80(6) 0.50(1)  13(2) Unknown Fe^(III)1.21(6) 1.77(9) 0.57(15)  7(2) Fe^(II) Fe₂(OH)_(0.6)(dobdc) 0.44(2)0.95(4) 0.41(4)  30(3) Fe^(III)—OH (1′) 1.08(1) 1.98(2) 0.44(3)  70(4)Fe^(II) Fe_(0.1)Mg_(1.9)(dobdc) 1.08(1) 2.25(1) 0.31(2) 100 Fe^(II) (2)Fe_(0.1)Mg_(1.9)(dobdc) 0.45(1) 1.08(3) 0.51(2)  89(4) Fe^(III)—OH(after N₂O/C₂H₆ 1.07(7) 2.24(11) 0.34(12)  11(3) Fe^(II) treatment)

The framework maintained both crystallinity and porosity afteroxidation, with a Brunauer-Emmett-Teller (BET) surface area of 1013 m²/gand a Langmuir surface area of 1171 m²/g. Rietveld analysis of powderX-ray diffraction data collected at 100 K on 2 firmly established thepresence of a new Fe—O bond, but did not reveal whether a hydrogen atomis present. However, the Fe—OH bond distance of 1.92(1) Å, which isconsistent with the bond lengths of previously reported octahedraliron(III)-hydroxide complexes (1.84-1.93 Å) (see FIG. 18B). In addition,the trans Fe-O_(axial) bond was slightly elongated (Fe—O_(axial)=2.20(1)Å; average Fe—O_(equatorial)=2.04(1) Å), with the iron center shiftedslightly out of the plane of the four equatorial oxygen atoms by 0.23(1)Å. EXAFS analysis of the same sample, as well as periodic DFTcalculations, provide bond lengths that were consistent with thoseobtained from the diffraction data (see TABLE 11 and TABLE 12).

TABLE 11 EXAFS curve fitting parameters for Fe₂(dobdc) and comparisonwith bond lengths obtained by PXRD. R (Å) Path PXRD EXAFS N σ² (Å²) R(%) Fe—O 2.10^(a) 2.06(1)  5 0.010(2) 1.0 Fe—C 3.05^(a) 3.07(5)  50.003(4) ΔΕ₀ = 3.1 Fe—Fe 3.00(2) 2.96(3)  2 0.010(6) Fe—OC 3.23^(a)3.22(8) 10 0.010(11)

TABLE 12 EXAFS curve fitting parameters for 2 and comparison with bondlengths obtained by DFT (periodic PBE + U) and PXRD (100K data). Notethat although the PXRD and EXAFS are in good agreement overall, thereare dissimilarities, especially in the Fe— Oaxial bond lengths for 2.This is because while EXAFS can be used to obtain first-shell distanceswith great accuracy, it is much more limited when resolution ofdifferent bond lengths is needed,especially when the scatterers haveboth a similar distance and atomic number, as is the case in 2. R (Å)Path DFT PXRD EXAFS N σ² (Å²) R (%) Fe—OH 1.84 1.92(1) 1.85(3)  10.009(1) 1.1 Fe—O_(eq) 2.02^(a) 2.04^(a) 2.02(1)  4 0.009(1) ΔΕ₀ = 2.70Fe—O_(ax) 2.27 2.20(1) 2.33(4)  1 0.009(1) Fe—C 3.01^(a) 3.03^(a)2.95(7)  5 0.009(1) Fe—Fe 3.23 3.16(1) 3.15(9)  2 0.016(4) Fe—O—C3.19^(a) 3.21^(a) 3.16(14) 10 0.006(8) Bold numbers are fixed values.Numbers in parentheses show uncertainty. ^(a)Averaged values.

Surprisingly, the iron(III)-hydroxide species was capable of activatingweak C—H bonds. When the partially oxidized sample 2′ was exposed to1,4-cyclohexadiene (C—H bond dissociation energy of 305 kJ/mol) at roomtemperature, benzene was produced as the sole product in quantitativeyield. In the process, the iron of the framework converted entirely backto iron(II), as determined by Mössbauer spectroscopy. Such reactivity israre for iron(III)-hydroxide compounds. For instance, lipoxygenase, anenzyme that converts 1,4-dienes into alkyl hydroperoxides, is believedto proceed through a non-heme ferric hydroxide intermediate, and severalmolecular lipoxygenase mimics have also been reported to activate theC—H bond of 1,4-cyclohexadiene and other 1,4-dienes.

Because the isolation of an iron(III)-hydroxide product from a reactionemploying a two-electron oxidant strongly suggests the intermediacy ofan iron(IV)-oxo species, the oxidation in the presence of a hydrocarbonsubstrate containing stronger C—H bonds, specifically ethane (C—H bonddissociation energy of 423 kJ/mol) was carried out, hoping to interceptthe oxo species before its decay. Indeed, flowing an N₂O:ethane:Armixture (10:25:65) over the framework at 75° C. led to the formation ofvarious ethane-derived oxygenates, including ethanol, acetaldehyde,diethyl ether, and other ether oligomers, as determined by 1H NMRspectroscopy of the extracted products. It was hypothesized that thecomplex mixture of products was related to the close proximity ofreactive iron centers, which are 8.75(2) Å and 6.84(1) Å apart acrossand along a channel, respectively, in 1. To avoid oligomerization andover-oxidation, a mixed-metal metal-organic framework,Fe_(0.1)Mg_(1.9)(dobdc) (3), in which the iron(II) sites are dilutedwith redox-inactive magnesium(II) centers, was synthesized. The BETsurface area of 1670 m²/g for this material falls between the surfaceareas of the pure iron and pure magnesium frameworks (1360 and 1800m²/g, respectively) While determining the exact distribution of metalcenters in heterometallic metal-organic frameworks is challenging, theunit cell parameters of 3 are also in between those of Fe₂(dobdc) andMg₂(dobdc) (see TABLE 13), suggesting the formation of a solid solutionrather than a mixture of two separate phases.

TABLE 13 Unit cell parameters (298K) of Fe₂(dobdc),Fe_(x)Mg_(2−x)(dobdc), and Mg₂(dobdc). The unit cell constants andvolumes of Fe_(0.1)Mg_(1.9)(dobdc) and Fe_(0.44)Mg_(1.56)(dobdc) are inbetween that of Fe₂(dobdc) and Mg₂(dobdc) and show a linear correlationwith magnesium content, in agreement with Vegard's Law for solidsolutions. Fe₂ Fe_(0.44)Mg_(1.56) Fe_(0.1)Mg_(1.9) Mg₂ (dobdc) (dobdc)(dobdc) (dobdc) a (Å)  26.1603(10)  25.9964(8)  25.9485(9)  25.9111(20)c (Å)   6.8657(4)   6.8465(4)   6.8574(4)   6.8687(12) V (Å³) 4069.1(3)4007.1(4) 3998.7(3) 3993.7(7)Additionally, the Mössbauer spectrum of 3 showed sharp doublets with asignificantly different quadrupole splitting than the all-iron analogue(2.25(1) mm/s versus 2.02(1) mm/s in Fe₂(dobdc); see TABLE 10),indicating that the iron centers in the magnesium-diluted framework werein an altered, but uniform, environment. Thus, 3 is likely bestdescribed as containing either isolated iron centers or short multi-ironsegments dispersed evenly throughout a magnesium-based framework.

Exposure of 3 to N₂O and ethane under the same flow-through conditionsyielded the exclusive formation of ethanol and acetaldehyde in a 10:1ratio, albeit in low yield (60% with respect to iron). Gaschromatography analysis of the headspace revealed no ethanol,acetaldehyde, or CO, suggesting the products remain bound to theframework (either at open iron or open magnesium sites), which wouldlikely explain the high ethanol selectivity. While the framework wasstill highly crystalline after N₂O/ethane treatment, Mössbauerspectroscopy revealed that roughly 90% of the iron centers have decayedinto a species with similar spectral parameters as 2 (see FIG. 5 andTABLE 10). It was postulated that the formation of iron(III)-hydroxideor alkoxide decay products prematurely halted the catalytic cycle,resulting in substoichiometric yields of hydroxylated product (see FIG.25). Because glass can be a source of H-atoms, the reaction wassubsequently repeated in a batch, rather than flow-through mode, in aTeflon-lined stainless-steel bomb, which produced both higher yieldswith respect to iron (turnover number=1.6) and selectivities (25:1ethanol:acetaldehyde), showing that the system can indeed be modestlycatalytic if competing substrates were excluded.

As the high reactivity of the iron-oxo species precluded isolation inboth Fe₂(dobdc) and its magnesium-diluted analog, electronic structurecalculations were performed on Fe₂(O)₂(dobdc) (4) to gain insight intothe geometric and electronic structure of iron-oxo units supportedwithin the framework. First, periodic PBE+U geometry optimizations wereperformed on 4 for the singlet, triplet, and quintet spin states. Aquintet ground state was predicted, with a short Fe—O bond length of1.64 Å, consistent with that of previously reported iron(IV)-oxocomplexes (see FIG. 26 and TABLE 14).

TABLE 14 Relative energies (kJ/mol)^(a) and Mulliken atomic spindensities on Fe and O1^(b) for 2 and 4. Full geometry optimizations wereperformed by periodic PBE + U for three possible spin states of each 2and 4. Spin Spin Fe—O1 density density Distance Relative energy Species2S on Fe on O1 (Å) (kJ/(mol Fe))^(a) 2 1 1.09 0.00 1.81 149.5 3 3.34−0.15 1.87 61.7 5 4.31 0.23 1.84 0.0 4 0 0.00 0.00 1.64 113.9 2 1.510.46 1.62 76.7 4 3.42 0.33 1.64 0.0 ^(a)The lowest-energy spin state foreach species has been taken as 0 reference. ^(b)O1 is the terminaloxygen as shown in FIG. 27.The periodic structure was then truncated to an 89-atom model clustercontaining three metal centers, six organic linkers, and an oxo moietyto facilitate calculations using more accurate methods. The clustercalculations were simplified by replacing the two peripheral iron(II)centers with closed-shell zinc(II) centers, which have the same chargeand a similar ionic radius to iron(II) and magnesium(II) cations (seeFIG. 27). The geometry of this cluster was then optimized for the groundstate, with all atoms except for the central iron and its firstcoordination sphere frozen at the coordinates from the periodic PBE+Uoptimization. As shown in TABLE 15, the M06 calculations also predict aquintet ground state.

TABLE 15 Calculated relative energies (kJ/mol) of the cluster model of4. S M06 CASPT2 0 210.6 249.4 1 136.4 127.6 2 0.0 0.0Further calculations were performed with several otherexchange-correlation functionals, and in each case the ground state wasfound to be a quintet (see TABLES 16-20).

TABLE 16 Relative energies (kJ/mol)^(a), S, S², and Mulliken spindensities on Fe and O1 for 2 and 4 cluster models. Single-pointcalculations were done on the 89- and 90-atom models using PBE/SDD(Fe,Zn), 6- 311 + G(2df, p)(C, H, O)//PBE/SDD(Fe, Zn), 6-31G(d)(C, H, O).Relative State Spin density energy Species 2M_(s) S S² Fe O1(kJ/mol)^(a) 2 1 0.67 1.12 0.97 0.13 52.1 (cluster 3 1.52 3.82 2.88 0.0332.6 model) 5 2.50 8.76 4.27 0.34 0.0 4 0 (open shell) 0.79 1.42 −0.080.07 88.4 (cluster 2 1.06 2.20 1.57 0.73 54.4 model) 4 2.01 6.06 3.080.60 0.0 6 3.01 12.01 3.97 1.16 104.8 ^(a)Relative energy is computedwith respect to the most stable spin state.

TABLE 17 Relative energies (kJ/mol)^(a), S, S², and Mulliken spindensities on Fe and O1 for 2 and 4 cluster models. Single-pointcalculations were done on the 89- and 90-atom models using M06/SDD(Fe,Zn), 6- 311 + G(2df, p)(C, H, O)//M06-L/SDD(Fe, Zn), 6-31G(d)(C, H, O).Relative State Spin density energy Species 2M_(s) S S² Fe O1(kJ/mol)^(a) 2 1 0.85 1.56 1.05 0.04 218.5 (cluster 3 1.53 3.87 3.11−0.13 109.6 model) 5 2.50 8.76 4.30 0.30 0.0 4 0 (open shell) 0.99 1.961.00 −1.10 210.6 (cluster 2 1.24 2.76 2.83 −0.39 136.4 model) 4 2.056.28 3.65 0.31 0.0 6 3.00 12.03 4.16 1.15 57.2 ^(a)Relative energy iscomputed with respect to the most stable spin state.

TABLE 18 Relative energies (kJ/mol)^(a), S, S², and Mulliken spindensities on Fe and O1 for 2 and 4 cluster models. Single- pointcalculations were done on the 89- and 90-atom models usingM08-SO/SDD(Fe, Zn), 6-311 + G(2df, p)(C, H, O)//M06-L/SDD(Fe, Zn),6-31G(d)(C, H, O). Relative State Spin density energy Species 2M_(s) SS² Fe O1 (kJ/mol)^(a) 2 1 1.01 2.02 1.02 0.01 115.8 (cluster 3 1.51 3.792.98 −0.07 82.5 model) 5 2.50 8.76 4.37 0.33 0.0 4 0 (open shell) 1.032.09 −0.99 1.02 124.2 (cluster 2 1.31 3.03 2.78 −0.87 86.8 model) 4 2.066.29 3.73 0.13 0.0 6 3.00 12.02 4.28 1.34 55.3 ^(a)Relative energy iscomputed with respect to the most stable spin state.

TABLE 19 Relative energies (kJ/mol)^(a), S, S², and Mulliken spindensities on Fe and O1 for 2 and 4 cluster models. Single- pointcalculations were done on the 89- and 90-atom models usingMPW1B95/SDD(Fe, Zn), 6-311 + G(2df, p)(C, H, O)//M06-L/SDD(Fe, Zn),6-31G(d)(C, H, O). Relative State Spin density energy Species 2M_(s) SS² Fe O1 (kJ/mol)^(a) 2 1 0.60 0.96 1.04 0.06 143.5 (cluster 3 1.53 3.883.07 −0.13 80.1 model) 5 2.50 8.76 4.34 0.29 0.0 4 0 (open shell) 0.801.44 0.72 −0.61 141.7 (cluster 2 1.24 2.79 2.87 −0.58 96.1 model) 4 2.066.29 3.69 0.14 0.0 6 3.00 12.02 4.21 1.20 45.3 ^(a)Relative energy iscomputed with respect to the most stable spin state.

TABLE 20 Relative energies (kJ/mol)^(a), S, S², and Mulliken spindensities on Fe and O1 for 2 and 4 cluster models. Single- pointcalculations were done on the 89- and 90-atom models usingPW6B95/SDD(Fe, Zn), 6-311 + G(2df, p)(C, H, O)//M06-L/SDD(Fe, Zn),6-31G(d)(C, H, O). Relative State Spin density energy Species 2M_(s) SS² Fe O1 (kJ/mol)^(a) 2 1 0.60 0.96 1.03 0.07 121.4 (cluster 3 1.53 3.873.04 −0.11 69.7 model) 5 2.50 8.76 4.32 0.30 0.0 4 0 (open shell) 0.801.43 0.64 −0.54 126.8 (cluster 2 1.23 2.74 2.79 −0.43 87.4 model) 4 2.056.25 3.61 0.25 0.0 6 3.00 12.03 4.18 1.17 50.3 ^(a)Relative energy iscomputed with respect to the most stable spin state.

Note that similar results were obtained when the Zn(II) centers in the89-atom cluster were replaced with Mg(II) centers (see TABLES 21 and22).

TABLE 21 Relative energies (kJ/mol)^(a), S, S², and Mulliken spindensities on Fe and O1 for the cluster model of 4 and the cluster modelof 4 with Zn(II) replacing Mg(II). All calculations were done usingM06-L/SDD(Fe, Zn), 6-31G(d)(C, H, O, Mg)/opt6. Relative State Spindensity Fe—O1 energy Species 2M_(s) S S² Fe O1 (Å) (kJ/mol)^(a) 4 0 0.771.36 0.27 −0.14 1.62 138.2 (cluster 2 1.15 2.48 2.02 0.44 1.61 77.3model with 4 2.04 6.22 3.31 0.60 1.64 0.0 Zn(II)) 4 0 0.78 1.40 0.26−0.11 1.62 138.7 (cluster 2 1.17 2.55 2.18 0.34 1.60 71.9 model with 42.06 6.29 3.35 0.61 1.64 0.0 Mg(II)) ^(a)Relative energy is computedwith respect to the most stable spin state.

TABLE 22 Relative energies (kJ/mol)^(a), S, S², and Mulliken spindensities on Fe and O1 for the cluster model of 4 and the cluster modelof 4 with Zn(II) replacing Mg(II). All calculations were done usingM06/SDD(Fe, Zn), 6-31G(d)(C, H, O, Mg)/opt6. Relative State Spin densityFe—O1 energy Species 2M_(s) S S² Fe O1 (Å) (kJ/mol)^(a) 4 0 0.86 1.600.41 −0.47 1.58 213.3 (cluster 2 1.27 2.90 2.90 −0.32 1.62 132.1 modelwith 4 2.05 6.27 3.54 0.42 1.63 0.0 Zn(II)) 4 0 0.91 1.73 −0.60 0.581.59 215.6 (cluster 2 1.29 2.97 2.91 −0.24 1.62 125.0 model with 4 2.076.38 3.61 0.46 1.64 0.0 Mg(II)) ^(a)Relative energy is computed withrespect to the most stable spin state.

The electronic structure of the cluster model of 4 was further examinedwith single-point multi-configurational complete active space (CASSCF)calculations followed by second-order perturbation theory (CASPT2).Again, the ground state was predicted to be the quintet state (see TABLE15 and TABLE 23).

TABLE 23 State energy splitting of 2 and 4 cluster models calculated byCASSCF and CASPT2. Largest Relative Relative CASSCF CASSCF CASPT2configuration energy energy Species 2M_(s) weight M^(a) (kJ/mol)(kJ/mol) 2 1  94% 0.102 328.4 294.6 (cluster 3  79% 0.309 216.7 145.2model) 5 100% 0.000 0.0 0.0 4 0 (open  77% 0.272 210.5 249.4 (clustershell) model) 2  74% 0.306 139.3 127.6 4  77% 0.311 0.0 0.0 ^(a)M is adiagnostic used to quantify the extent of multi-reference character ofthe system, and it is defined to be$M = {\frac{1}{2}\left( {2 - {n({MCDONO})} + {\sum\limits_{j = 1}^{n_{SOMO}}{{{n(j)} - 1}}} + {n({MCUNO})}} \right)}$where n(MCDONC), n_(SOMO), and n(MCUNC) are the most correlated doublyoccupied natural orbital, a singly occupied natural orbital, and themost correlating unoccupied natural orbital, respectively.

Both M06 and CASPT2 yield a spin density of 3.7 on iron, consistent withfour unpaired spins mainly localized on the metal (see TABLE 17 andTABLE 24).

TABLE 24 Charge and spin densities of the sextet and quintet ground spinstates of the cluster models of 2 and 4 from CASSCF calculations. 2 4(cluster model) (cluster model) Fe O1 Fe O1 CASSCF Mulliken Spin Density4.79 0.07 3.744 0.173 CASSCF Mulliken Charge 1.95 −0.77 1.765 −0.419Density CASSCF LoProp Charge Density 2.21 −1.09 1.963 −0.559Density functional and CASPT2 calculations were also performed on thecluster model of 2; all calculations led to a high-spin sextet groundstate for the iron(III) center (see TABLES 16-20 and Table 23).

A number of embodiments have been described herein. Nevertheless, itwill be understood that various modifications may be made withoutdeparting from the spirit and scope of this disclosure. Accordingly,other embodiments are within the scope of the following claims.

What is claimed is:
 1. A metal organic framework (MOF) that comprises aplurality of redox-active metals or metal ions connected by a pluralityof organic linking ligands comprising the structure(s) selected from thegroup consisting of:

wherein R¹-R¹⁴ are independently selected from H, D, halo, optionallysubstituted FG, optionally substituted (C₁-C₂₀)alkyl, optionallysubstituted (C₁-C₁₉)heteroalkyl, optionally substituted (C₁-C₂₀)alkenyl,optionally substituted (C₁-C₁₉)heteroalkenyl, optionally substituted(C₁-C₁₉)alkynyl, optionally substituted (C₁-C₁₉)heteroalkynyl,optionally substituted (C₁-C₁₉)cycloalkyl, optionally substituted(C₁-C₁₉)cycloalkenyl, optionally substituted aryl, optionallysubstituted heterocycle, optionally substituted mixed ring system,wherein one or more adjacent R groups can be linked together to form oneor more substituted rings selected from the group comprising cycloalkyl,cycloalkenyl, heterocycle, aryl, and mixed ring system; wherein, the MOFis capable of catalytically oxidizing of small hydrocarbons to theircorresponding alcohols and aldehydes
 2. The MOF of claim 1, wherein theorganic linking ligand comprises a structure selected from the groupconsisting of:

wherein


3. The MOF of claim 1, wherein the organic linking ligand is selectedfrom:


4. The MOF of claim 1, wherein the MOF comprises repeating units of theformula (M¹)₂(dobdc), of the formula (M¹)₂(m-dobdc) and/or of theformula (M¹)₂(H₄dotpdc^(R)), wherein M¹ is a redox-active metal or metalion.
 5. The MOF of claim 1, wherein the redox-active metal is selectedfrom Fe, Mn, Co, Ni, and Cu, or a divalent cation of any of theforegoing
 6. The MOF of claim 1, wherein the MOF is a mixed metal MOFand comprises a plurality of redox-active metal ions and a plurality ofredox-inactive metal ions.
 7. The MOF of claim 6, wherein the pluralityof redox-inactive metal ions is selected from Mg, Ca, Sr, Ba, Sc, Y, Ti,Zr, V, Nb, Ta, Cr, Mo, W, Re, Ru, Os, Rh, Ir, Pd, Pt, Ag, Au, Zn, Cd,Hg, Al, Ga, In, Si, Ge, Sn, Pb, As, Te, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb,Db, Tm, Yb, and La, or a divalent cation of any of the foregoing.
 8. TheMOF of claim 1, wherein the MOF comprises repeating units of the formula(M¹)_(x)(M²)_(2-x)(dobdc), of the formula ((M¹)_(x)(M²)_(2-x)(m-dobdc)and/or of the formula (M¹)_(x)(M²)_(2-x)(H₄dotpdc^(R)), wherein at leastone of M¹-M² is a redox-active metal or metal ion, x is a number lessthan or equal to
 1. 9. The MOF of claim 8, wherein the MOF comprisesrepeating units of the formula (M¹)_(x)(M²)_(2-x)(dobdc), of the formulaM¹)_(x)(M²)_(2-x)(m-dobdc) and/or of the formula(M¹)_(x)(M²)_(2-x)(H₄dotpdc^(R)) wherein at least one of M¹-M² is aredox-active metal or metal ion, x is a number less than or equal to0.3.
 10. The MOF of claim 9, wherein the MOF comprises repeating unitsof the formula (M¹)_(x)(M²)_(2-x)(dobdc), of the formulaM¹)_(x)(M²)_(2-x)(m-dobdc) and/or of the formula(M¹)_(x)(M²)_(2-x)(H₄dotpdc^(R)) wherein at least one of M¹-M² is aredox-active metal or metal ion, x is a number less than or equal to0.1.
 11. The MOF of claim 8, wherein M¹ is selected from Fe, Mn, Co, Ni,and Cu, or a divalent cation of any of the foregoing, and M² is selectedfrom Mg, Ca, Sr, Ba, Sc, Y, Ti, Zr, V, Nb, Ta, Cr, Mo, W, Re, Ru, Os,Rh, Ir, Pd, Pt, Ag, Au, Zn, Cd, Hg, Al, Ga, In, Si, Ge, Sn, Pb, As, Te,La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Db, Tm, Yb, and La, or a divalent cationof any of the foregoing.
 12. The MOF of claim 1, wherein the MOF isreacted with a terminal oxidant.
 13. The MOF of claim 12, wherein theterminal oxidant is N₂O.
 14. The MOF of claim 13, wherein the MOF isreacted with N₂O at a temperature of about 75° C. and at a pressurebetween 1 to 10 bar).
 15. A catalytic device comprising a MOF ofclaim
 1. 16. The device of claim 15, wherein the device comprises acolumn or bed which comprises the MOF.
 17. A method of oxidizing amolecule or compound, comprising contacting the molecule or compoundwith a MOF of claim
 1. 18. The method of claim 17, wherein the moleculeor compound is a C₁-C₆ alkane, a C₁-C₆ alkene, a C₁-C₆ alkyne, benzene,or a C₃-C₆ cycloalkyl.
 19. The method of claim 18, wherein the C₁-C₆alkane is converted to a corresponding C₁-C₆ alcohol or C₁-C₆ aldehyde.20. The method of claim 19, wherein the C₁-C₆ alkane is selectivelyconverted to the C₁-C₆ alcohol versus the C₁-C₆ aldehyde in a ratio of25:1.
 21. The method of claim 18, wherein the C₁-C₆ alkene is convertedto a C₁-C₆ corresponding epoxide.
 22. The method of claim 18, whereincyclohexane is converted into KA oil.